started porting nest, flatten and pack_structure_as already work

src/TensorFlowNET.Core/Util/nest.py.cs

@@ -0,0 +1,871 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using NumSharp;
+
+namespace Tensorflow.Util
+{
+    //Functions for working with arbitrarily nested sequences of elements.
+
+    //This module can perform operations on nested structures. A nested structure is a
+    //Python sequence, tuple (including `namedtuple`), or dict that can contain
+    //further sequences, tuples, and dicts.
+
+    //The utilities here assume (and do not check) that the nested structures form a
+    //'tree', i.e., no references in the structure of the input of these functions
+    //should be recursive.
+
+    //Example structures: `((3, 4), 5, (6, 7, (9, 10), 8))`, `(np.array(0),
+    //  (np.array([3, 4]), tf.constant([3, 4])))`
+    //
+
+    public static class nest
+    {
+
+
+        //def _get_attrs_values(obj):
+        //  """Returns the list of values from an attrs instance."""
+        //  attrs = getattr(obj.__class__, "__attrs_attrs__")
+        //  return [getattr(obj, a.name) for a in attrs]
+
+        /// <summary>
+        /// Returns a sorted list of the dict keys, with error if keys not sortable.
+        /// </summary>
+        private static IEnumerable<string> _sorted(IDictionary dict_)
+        {
+            return dict_.Keys.OfType<string>().OrderBy(x => x);
+        }
+
+
+        //def _is_namedtuple(instance, strict=False):
+        //  """Returns True iff `instance` is a `namedtuple`.
+
+        //  Args:
+        //    instance: An instance of a Python object.
+        //    strict: If True, `instance` is considered to be a `namedtuple` only if
+        //        it is a "plain" namedtuple. For instance, a class inheriting
+        //        from a `namedtuple` will be considered to be a `namedtuple`
+        //        iff `strict=False`.
+
+        //  Returns:
+        //    True if `instance` is a `namedtuple`.
+        //  """
+        //  return _pywrap_tensorflow.IsNamedtuple(instance, strict)
+
+
+        //# See the swig file (util.i) for documentation.
+        //_is_mapping = _pywrap_tensorflow.IsMapping
+        //_is_attrs = _pywrap_tensorflow.IsAttrs
+
+        /// <summary>
+        /// Converts the sequence `args` to the same type as `instance`.
+        /// </summary>
+        /// <param name="instance">an instance of `tuple`, `list`, `namedtuple`, `dict`, or
+        /// `collections.OrderedDict`.</param>
+        /// <param name="args">elements to be converted to the `instance` type.</param>
+        /// <returns>`args` with the type of `instance`.</returns>
+        private static object _sequence_like(object instance, IEnumerable<object> args)
+        {
+            if (is_mapping(instance))
+            {
+                //# Pack dictionaries in a deterministic order by sorting the keys.
+                //# Notice this means that we ignore the original order of `OrderedDict`
+                //# instances. This is intentional, to avoid potential bugs caused by mixing
+                //# ordered and plain dicts (e.g., flattening a dict but using a
+                //# corresponding `OrderedDict` to pack it back).
+                //    result = dict(zip(_sorted(instance), args))
+                //    return type(instance)((key, result[key]) for key in _six.iterkeys(instance))
+            }
+            //else if( _is_namedtuple(instance) || _is_attrs(instance)) 
+            //    return type(instance)(*args)
+            else
+            {
+                // Not a namedtuple
+                switch (instance)
+                {
+                    case object[] array:
+                        var result_array = new object[args.Count()];
+                        int i = 0;
+                        foreach (var x in args)
+                        {
+                            result_array[i] = x;
+                            i++;
+                        }
+                        return result_array;
+                    case List<object> list:
+                        return new List<object>(args);
+                    default:
+                        throw new TypeError("Type of sequence not supported (yet): " + instance.GetType());
+                }
+            }
+            throw new TypeError("Type of sequence not supported (yet): " + instance.GetType());
+        }
+
+        /// <summary>
+        /// Yields the next value from the given iterable.
+        /// </summary>
+        private static IEnumerable<object> _yield_value(object iterable)
+        {
+            if (is_mapping(iterable))
+            {
+                var dict = iterable as IDictionary;
+                //# Iterate through dictionaries in a deterministic order by sorting the
+                //# keys. Notice this means that we ignore the original order of `OrderedDict`
+                //# instances. This is intentional, to avoid potential bugs caused by mixing
+                //# ordered and plain dicts (e.g., flattening a dict but using a
+                //# corresponding `OrderedDict` to pack it back).
+                foreach (var key in _sorted(dict))
+                    yield return dict[key];
+            }
+            //else if (_is_attrs(iterable))
+            //{
+            //    //    for value in _get_attrs_values(iterable):
+            //    //      yield value
+            //}
+            else if (iterable is IEnumerable)
+            {
+                var enumerable = iterable as IEnumerable;
+                foreach (var value in enumerable)
+                    yield return value;
+            }
+            else
+            {
+                throw new TypeError("Unexpected iterable type: " + iterable.GetType());
+                //var jobj = JObject.FromObject(iterable);
+                //foreach (var key in _sorted())
+                //    yield return jobj[key];
+            }
+        }
+
+        //# See the swig file (util.i) for documentation.
+        public static bool is_sequence(object arg) => arg is IEnumerable && !(arg is string);
+
+        public static bool is_mapping(object arg) => arg is IDictionary;
+
+        //# See the swig file (util.i) for documentation.
+        //flatten = _pywrap_tensorflow.Flatten
+
+        public static List<object> flatten(object structure)
+        {
+            var list = new List<object>();
+            _flatten_recursive(structure, list);
+            return list;
+        }
+
+        private static void _flatten_recursive(object obj, List<object> list)
+        {
+            if (obj is string)
+            {
+                list.Add(obj);
+                return;
+            }
+            if (obj is IDictionary)
+            {
+                var dict = obj as IDictionary;
+                foreach (var key in _sorted(dict))
+                    _flatten_recursive(dict[key], list);
+                return;
+            }
+            if (obj is NDArray)
+            {
+                list.Add(obj);
+                return;
+            }
+            if (obj is IEnumerable)
+            {
+                var structure = obj as IEnumerable;
+                foreach (var child in structure)
+                    _flatten_recursive(child, list);
+                return;
+            }
+            list.Add(obj);
+        }
+
+
+        //# See the swig file (util.i) for documentation.
+        //_same_namedtuples = _pywrap_tensorflow.SameNamedtuples
+
+
+        //class _DotString(object):
+
+        //  def __str__(self):
+        //    return "."
+
+        //  def __repr__(self):
+        //    return "."
+
+
+        //_DOT = _DotString()
+
+
+        //def assert_same_structure(nest1, nest2, check_types=True):
+        //  """Asserts that two structures are nested in the same way.
+
+        //  Note that namedtuples with identical name and fields are always considered
+        //  to have the same shallow structure (even with `check_types=True`).
+        //  For intance, this code will print `True`:
+
+        //  ```python
+        //  def nt(a, b):
+        //    return collections.namedtuple('foo', 'a b')(a, b)
+        //  print(assert_same_structure(nt(0, 1), nt(2, 3)))
+        //  ```
+
+        //  Args:
+        //    nest1: an arbitrarily nested structure.
+        //    nest2: an arbitrarily nested structure.
+        //    check_types: if `True` (default) types of sequences are checked as well,
+        //        including the keys of dictionaries. If set to `False`, for example a
+        //        list and a tuple of objects will look the same if they have the same
+        //        size. Note that namedtuples with identical name and fields are always
+        //        considered to have the same shallow structure. Two types will also be
+        //        considered the same if they are both list subtypes (which allows "list"
+        //        and "_ListWrapper" from checkpointable dependency tracking to compare
+        //        equal).
+
+        //  Raises:
+        //    ValueError: If the two structures do not have the same number of elements or
+        //      if the two structures are not nested in the same way.
+        //    TypeError: If the two structures differ in the type of sequence in any of
+        //      their substructures. Only possible if `check_types` is `True`.
+        //  """
+        //  try:
+        //    _pywrap_tensorflow.AssertSameStructure(nest1, nest2, check_types)
+        //  except (ValueError, TypeError) as e:
+        //    str1 = str(map_structure(lambda _: _DOT, nest1))
+        //    str2 = str(map_structure(lambda _: _DOT, nest2))
+        //    raise type(e)("%s\n"
+        //                  "Entire first structure:\n%s\n"
+        //                  "Entire second structure:\n%s"
+        //                  % (str(e), str1, str2))
+
+
+        //def flatten_dict_items(dictionary):
+        //  """Returns a dictionary with flattened keys and values.
+
+        //  This function flattens the keys and values of a dictionary, which can be
+        //  arbitrarily nested structures, and returns the flattened version of such
+        //  structures:
+
+        //  ```python
+        //  example_dictionary = {(4, 5, (6, 8)): ("a", "b", ("c", "d"))}
+        //  result = {4: "a", 5: "b", 6: "c", 8: "d"}
+        //  flatten_dict_items(example_dictionary) == result
+        //  ```
+
+        //  The input dictionary must satisfy two properties:
+
+        //  1. Its keys and values should have the same exact nested structure.
+        //  2. The set of all flattened keys of the dictionary must not contain repeated
+        //     keys.
+
+        //  Args:
+        //    dictionary: the dictionary to zip
+
+        //  Returns:
+        //    The zipped dictionary.
+
+        //  Raises:
+        //    TypeError: If the input is not a dictionary.
+        //    ValueError: If any key and value have not the same structure, or if keys are
+        //      not unique.
+        //  """
+        //  if not isinstance(dictionary, (dict, _collections.Mapping)):
+        //    raise TypeError("input must be a dictionary")
+        //  flat_dictionary = {}
+        //  for i, v in _six.iteritems(dictionary):
+        //    if not is_sequence(i):
+        //      if i in flat_dictionary:
+        //        raise ValueError(
+        //            "Could not flatten dictionary: key %s is not unique." % i)
+        //      flat_dictionary[i] = v
+        //    else:
+        //      flat_i = flatten(i)
+        //      flat_v = flatten(v)
+        //      if len(flat_i) != len(flat_v):
+        //        raise ValueError(
+        //            "Could not flatten dictionary. Key had %d elements, but value had "
+        //            "%d elements. Key: %s, value: %s."
+        //            % (len(flat_i), len(flat_v), flat_i, flat_v))
+        //      for new_i, new_v in zip(flat_i, flat_v):
+        //        if new_i in flat_dictionary:
+        //          raise ValueError(
+        //              "Could not flatten dictionary: key %s is not unique."
+        //              % (new_i))
+        //        flat_dictionary[new_i] = new_v
+        //  return flat_dictionary
+
+        /// <summary>
+        /// Helper function for pack_sequence_as.
+        /// </summary>
+        /// <param name="structure">Substructure (list / tuple / dict) to mimic.</param>
+        /// <param name="flat">Flattened values to output substructure for.</param>
+        /// <param name="index">Index at which to start reading from flat.</param>
+        /// <returns>
+        /// The tuple(new_index, child), where:
+        ///  * new_index - the updated index into `flat` having processed `structure`.
+        ///  * packed - the subset of `flat` corresponding to `structure`,
+        /// having started at `index`, and packed into the same nested
+        /// format.</returns>
+        private static (int new_index, List<object> child) _packed_nest_with_indices(object structure, List<object> flat,
+            int index)
+        {
+            var packed = new List<object>();
+            foreach (var s in _yield_value(structure))
+            {
+                if (is_sequence(s))
+                {
+                    var (new_index, child) = _packed_nest_with_indices(s, flat, index);
+                    packed.Add(_sequence_like(s, child));
+                    index = new_index;
+                }
+                else
+                {
+                    packed.Add(flat[index]);
+                    index += 1;
+                }
+            }
+            return (index, packed);
+        }
+
+        private static int len(IEnumerable<object> x) => x.Count();
+
+        /// <summary>
+        /// Returns a given flattened sequence packed into a given structure.
+        /// If `structure` is a scalar, `flat_sequence` must be a single-element list;
+        /// in this case the return value is `flat_sequence[0]`.
+        /// 
+        /// If `structure` is or contains a dict instance, the keys will be sorted to
+        /// pack the flat sequence in deterministic order. This is true also for
+        /// `OrderedDict` instances: their sequence order is ignored, the sorting order of
+        /// keys is used instead. The same convention is followed in `flatten`.
+        /// This correctly repacks dicts and `OrderedDict`s after they have been
+        /// flattened, and also allows flattening an `OrderedDict` and then repacking it
+        /// back using a corresponding plain dict, or vice-versa.
+        /// Dictionaries with non-sortable keys cannot be flattened.
+        /// </summary>
+        /// <param name="structure">
+        /// Nested structure, whose structure is given by nested lists,
+        /// tuples, and dicts. Note: numpy arrays and strings are considered
+        /// scalars.
+        /// </param>
+        /// <param name="flat_sequence"> flat sequence to pack.</param>
+        /// <returns> `flat_sequence` converted to have the same recursive structure as
+        /// `structure`.
+        /// </returns>
+        public static object pack_sequence_as(object structure, List<object> flat_sequence)
+        {
+            if (flat_sequence == null)
+                throw new ArgumentException("flat_sequence must not be null");
+            //  if not is_sequence(flat_sequence):
+            //    raise TypeError("flat_sequence must be a sequence")
+
+            if (!is_sequence(structure))
+            {
+                if (len(flat_sequence) != 1)
+                    throw new ValueError($"Structure is a scalar but len(flat_sequence) ==  {len(flat_sequence)} > 1");
+                return flat_sequence.FirstOrDefault();
+            }
+            int final_index = 0;
+            List<object> packed = null;
+            try
+            {
+                (final_index, packed) = _packed_nest_with_indices(structure, flat_sequence, 0);
+                if (final_index < len(flat_sequence))
+                    throw new IndexOutOfRangeException($"Final index: { final_index} was smaller than  len(flat_sequence): { len(flat_sequence) }");
+            }
+            catch (IndexOutOfRangeException)
+            {
+                var flat_structure = flatten(structure);
+                if (len(flat_structure) != len(flat_sequence))
+                {
+                    throw new ValueError("Could not pack sequence. Structure had %d elements, but " +
+                                         $"flat_sequence had {len(flat_structure)} elements. flat_sequence had: {len(flat_sequence)}");
+                }
+                return _sequence_like(structure, packed);
+            }
+            return packed;
+        }
+
+        /// <summary>
+        /// Applies `func` to each entry in `structure` and returns a new structure.
+        ///
+        ///  Applies `func(x[0], x[1], ...)` where x[i] is an entry in
+        ///  `structure[i]`.  All structures in `structure` must have the same arity,
+        ///  and the return value will contain the results in the same structure.
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <typeparam name="U"></typeparam>
+        /// <param name="func"> A callable that accepts as many arguments as there are structures.</param>
+        /// <param name="structure">scalar, or tuple or list of constructed scalars and/or other
+        ///      tuples/lists, or scalars.  Note: numpy arrays are considered as scalars.</param>
+        /// <param name="check_types">If set to
+        ///      `True` (default) the types of iterables within the structures have to be
+        ///      same (e.g. `map_structure(func, [1], (1,))` raises a `TypeError`
+        ///     exception). To allow this set this argument to `False`.
+        ///      Note that namedtuples with identical name and fields are always
+        ///      considered to have the same shallow structure.</param>
+        /// <returns>
+        ///    A new structure with the same arity as `structure`, whose values correspond
+        ///    to `func(x[0], x[1], ...)` where `x[i]` is a value in the corresponding
+        ///    location in `structure[i]`. If there are different sequence types and
+        ///    `check_types` is `False` the sequence types of the first structure will be
+        ///    used.
+        /// </returns>
+        public static IEnumerable<U> map_structure<T, U>(Func<T, U> func, IEnumerable<T> structure, bool check_types = false)
+        {
+
+            //  for other in structure[1:]:
+            //    assert_same_structure(structure[0], other, check_types=check_types)
+
+            //  flat_structure = [flatten(s) for s in structure]
+            //  entries = zip(*flat_structure)
+
+            //  return pack_sequence_as(
+            //      structure[0], [func(*x) for x in entries])
+            return null;
+        }
+
+        //def map_structure_with_paths(func, *structure, **kwargs):
+        //  """Applies `func` to each entry in `structure` and returns a new structure.
+
+        //  Applies `func(path, x[0], x[1], ..., **kwargs)` where x[i] is an entry in
+        //  `structure[i]` and `path` is the common path to x[i] in the structures.  All
+        //  structures in `structure` must have the same arity, and the return value will
+        //  contain the results in the same structure. Special kwarg `check_types`
+        //  determines whether the types of iterables within the structure must be the
+        //  same-- see **kwargs definition below.
+
+        //  Args:
+        //    func: A callable with the signature func(path, *values, **kwargs) that is
+        //      evaluated on the leaves of the structure.
+        //    *structure: A variable number of compatible structures to process.
+        //    **kwargs: Optional kwargs to be passed through to func. Special kwarg
+        //      `check_types` is not passed to func, but instead determines whether the
+        //      types of iterables within the structures have to be same (e.g.,
+        //      `map_structure(func, [1], (1,))` raises a `TypeError` exception). By
+        //      default, the types must match. To allow iteration over structures of
+        //      different types (but common arity), set this kwarg to `False`.
+
+        //  Returns:
+        //    A structure of the same form as the input structures whose leaves are the
+        //    result of evaluating func on corresponding leaves of the input structures.
+
+        //  Raises:
+        //    TypeError: If `func` is not callable or if the structures do not match
+        //      each other by depth tree.
+        //    TypeError: If `check_types` is not `False` and the two structures differ in
+        //      the type of sequence in any of their substructures.
+        //    ValueError: If no structures are provided.
+        //  """
+        //  if not callable(func):
+        //    raise TypeError("func must be callable, got: %s" % func)
+        //  if not structure:
+        //    raise ValueError("Must provide at least one structure")
+
+        //  check_types = kwargs.pop("check_types", True)
+        //  for other in structure[1:]:
+        //    assert_same_structure(structure[0], other, check_types=check_types)
+
+        //# First set paths_and_values to:
+        //# [[(p11, v11), ... (p1n, v1n)], ... [(pm1, vm1), ... (pmn, vmn)]]
+        //  paths_and_values = [flatten_with_joined_string_paths(s) for s in structure]
+
+        //# Now zip(*paths_and_values) would be:
+        //# [((p11, v11), ... (pm1, vm1)), ... ((p1n, v1n), ... (pmn, vmn))]
+        //# so grouped_by_path is set to:
+        //# [[(p11, ... pm1), (v11, ... vm1)], ... [(p1n, ... pmn), (v1n, ... vmn)]]
+        //# Note that p1i, ... pmi must all be equal since the structures are the same.
+        //  grouped_by_path = [zip(*p_v) for p_v in zip(*paths_and_values)]
+
+        //  return pack_sequence_as(structure[0], [
+        //      func(paths[0], *values, **kwargs) for paths, values in grouped_by_path])
+
+
+        //def _yield_flat_up_to(shallow_tree, input_tree):
+        //  """Yields elements `input_tree` partially flattened up to `shallow_tree`."""
+        //  if is_sequence(shallow_tree):
+        //    for shallow_branch, input_branch in zip(_yield_value(shallow_tree),
+        //                                            _yield_value(input_tree)):
+        //      for input_leaf in _yield_flat_up_to(shallow_branch, input_branch):
+        //        yield input_leaf
+        //  else:
+        //    yield input_tree
+
+
+        //def assert_shallow_structure(shallow_tree, input_tree, check_types=True):
+        //  """Asserts that `shallow_tree` is a shallow structure of `input_tree`.
+
+        //  That is, this function tests if the `input_tree` structure can be created from
+        //  the `shallow_tree` structure by replacing its leaf nodes with deeper
+        //  tree structures.
+
+        //  Examples:
+
+        //  The following code will raise an exception:
+        //  ```python
+        //    shallow_tree = ["a", "b"]
+        //    input_tree = ["c", ["d", "e"], "f"]
+        //    assert_shallow_structure(shallow_tree, input_tree)
+        //  ```
+
+        //  The following code will not raise an exception:
+        //  ```python
+        //    shallow_tree = ["a", "b"]
+        //    input_tree = ["c", ["d", "e"]]
+        //    assert_shallow_structure(shallow_tree, input_tree)
+        //  ```
+
+        //  Args:
+        //    shallow_tree: an arbitrarily nested structure.
+        //    input_tree: an arbitrarily nested structure.
+        //    check_types: if `True` (default) the sequence types of `shallow_tree` and
+        //      `input_tree` have to be the same. Note that even with check_types==True,
+        //      this function will consider two different namedtuple classes with the same
+        //      name and _fields attribute to be the same class.
+
+        //  Raises:
+        //    TypeError: If `shallow_tree` is a sequence but `input_tree` is not.
+        //    TypeError: If the sequence types of `shallow_tree` are different from
+        //      `input_tree`. Only raised if `check_types` is `True`.
+        //    ValueError: If the sequence lengths of `shallow_tree` are different from
+        //      `input_tree`.
+        //  """
+        //  if is_sequence(shallow_tree):
+        //    if not is_sequence(input_tree):
+        //      raise TypeError(
+        //          "If shallow structure is a sequence, input must also be a sequence. "
+        //          "Input has type: %s." % type(input_tree))
+
+        //    if check_types and not isinstance(input_tree, type(shallow_tree)):
+        //# Duck-typing means that nest should be fine with two different
+        //# namedtuples with identical name and fields.
+        //      shallow_is_namedtuple = _is_namedtuple(shallow_tree, False)
+        //      input_is_namedtuple = _is_namedtuple(input_tree, False)
+        //      if shallow_is_namedtuple and input_is_namedtuple:
+        //        if not _same_namedtuples(shallow_tree, input_tree):
+        //          raise TypeError(
+        //              "The two namedtuples don't have the same sequence type. Input "
+        //              "structure has type %s, while shallow structure has type %s."
+        //              % (type(input_tree), type(shallow_tree)))
+        //      elif not (isinstance(shallow_tree, _collections.Mapping)
+        //                and isinstance(input_tree, _collections.Mapping)):
+        //        raise TypeError(
+        //            "The two structures don't have the same sequence type. Input "
+        //            "structure has type %s, while shallow structure has type %s."
+        //            % (type(input_tree), type(shallow_tree)))
+
+        //    if len(input_tree) != len(shallow_tree):
+        //      raise ValueError(
+        //          "The two structures don't have the same sequence length. Input "
+        //          "structure has length %s, while shallow structure has length %s."
+        //          % (len(input_tree), len(shallow_tree)))
+
+        //    if check_types and isinstance(shallow_tree, (dict, _collections.Mapping)):
+        //      if set(input_tree) != set(shallow_tree):
+        //        raise ValueError(
+        //            "The two structures don't have the same keys. Input "
+        //            "structure has keys %s, while shallow structure has keys %s." %
+        //            (list(_six.iterkeys(input_tree)),
+        //             list(_six.iterkeys(shallow_tree))))
+
+        //      input_tree = list(sorted(_six.iteritems(input_tree)))
+        //      shallow_tree = list(sorted(_six.iteritems(shallow_tree)))
+
+        //    for shallow_branch, input_branch in zip(shallow_tree, input_tree):
+        //      assert_shallow_structure(shallow_branch, input_branch,
+        //                               check_types=check_types)
+
+
+        //def flatten_up_to(shallow_tree, input_tree):
+        //  """Flattens `input_tree` up to `shallow_tree`.
+
+        //  Any further depth in structure in `input_tree` is retained as elements in the
+        //  partially flatten output.
+
+        //  If `shallow_tree` and `input_tree` are not sequences, this returns a
+        //  single-element list: `[input_tree]`.
+
+        //  Use Case:
+
+        //  Sometimes we may wish to partially flatten a nested sequence, retaining some
+        //  of the nested structure. We achieve this by specifying a shallow structure,
+        //  `shallow_tree`, we wish to flatten up to.
+
+        //  The input, `input_tree`, can be thought of as having the same structure as
+        //  `shallow_tree`, but with leaf nodes that are themselves tree structures.
+
+        //  Examples:
+
+        //  ```python
+        //  input_tree = [[[2, 2], [3, 3]], [[4, 9], [5, 5]]]
+        //  shallow_tree = [[True, True], [False, True]]
+
+        //  flattened_input_tree = flatten_up_to(shallow_tree, input_tree)
+        //  flattened_shallow_tree = flatten_up_to(shallow_tree, shallow_tree)
+
+        //# Output is:
+        //# [[2, 2], [3, 3], [4, 9], [5, 5]]
+        //# [True, True, False, True]
+        //  ```
+
+        //  ```python
+        //  input_tree = [[('a', 1), [('b', 2), [('c', 3), [('d', 4)]]]]]
+        //  shallow_tree = [['level_1', ['level_2', ['level_3', ['level_4']]]]]
+
+        //  input_tree_flattened_as_shallow_tree = flatten_up_to(shallow_tree, input_tree)
+        //  input_tree_flattened = flatten(input_tree)
+
+        //# Output is:
+        //# [('a', 1), ('b', 2), ('c', 3), ('d', 4)]
+        //# ['a', 1, 'b', 2, 'c', 3, 'd', 4]
+        //  ```
+
+        //  Non-Sequence Edge Cases:
+
+        //  ```python
+        //  flatten_up_to(0, 0)  # Output: [0]
+        //  flatten_up_to(0, [0, 1, 2])  # Output: [[0, 1, 2]]
+        //  flatten_up_to([0, 1, 2], 0)  # Output: TypeError
+        //  flatten_up_to([0, 1, 2], [0, 1, 2])  # Output: [0, 1, 2]
+        //  ```
+
+        //  Args:
+        //    shallow_tree: a possibly pruned structure of input_tree.
+        //    input_tree: an arbitrarily nested structure or a scalar object.
+        //      Note, numpy arrays are considered scalars.
+
+        //  Returns:
+        //    A Python list, the partially flattened version of `input_tree` according to
+        //    the structure of `shallow_tree`.
+
+        //  Raises:
+        //    TypeError: If `shallow_tree` is a sequence but `input_tree` is not.
+        //    TypeError: If the sequence types of `shallow_tree` are different from
+        //      `input_tree`.
+        //    ValueError: If the sequence lengths of `shallow_tree` are different from
+        //      `input_tree`.
+        //  """
+        //  assert_shallow_structure(shallow_tree, input_tree)
+        //  return list(_yield_flat_up_to(shallow_tree, input_tree))
+
+
+        //def map_structure_up_to(shallow_tree, func, *inputs):
+        //  """Applies a function or op to a number of partially flattened inputs.
+
+        //  The `inputs` are flattened up to `shallow_tree` before being mapped.
+
+        //  Use Case:
+
+        //  Sometimes we wish to apply a function to a partially flattened
+        //  sequence (for example when the function itself takes sequence inputs). We
+        //  achieve this by specifying a shallow structure, `shallow_tree` we wish to
+        //  flatten up to.
+
+        //  The `inputs`, can be thought of as having the same structure as
+        //  `shallow_tree`, but with leaf nodes that are themselves tree structures.
+
+        //  This function therefore will return something with the same base structure as
+        //  `shallow_tree`.
+
+        //  Examples:
+
+        //  ```python
+        //  ab_tuple = collections.namedtuple("ab_tuple", "a, b")
+        //  op_tuple = collections.namedtuple("op_tuple", "add, mul")
+        //  inp_val = ab_tuple(a=2, b=3)
+        //  inp_ops = ab_tuple(a=op_tuple(add=1, mul=2), b=op_tuple(add=2, mul=3))
+        //  out = map_structure_up_to(inp_val, lambda val, ops: (val + ops.add) * ops.mul,
+        //                            inp_val, inp_ops)
+
+        //# Output is: ab_tuple(a=6, b=15)
+        //  ```
+
+        //  ```python
+        //  data_list = [[2, 4, 6, 8], [[1, 3, 5, 7, 9], [3, 5, 7]]]
+        //  name_list = ['evens', ['odds', 'primes']]
+        //  out = map_structure_up_to(
+        //      name_list,
+        //      lambda name, sec: "first_{}_{}".format(len(sec), name),
+        //      name_list, data_list)
+
+        //# Output is: ['first_4_evens', ['first_5_odds', 'first_3_primes']]
+        //  ```
+
+        //  Args:
+        //    shallow_tree: a shallow tree, common to all the inputs.
+        //    func: callable which will be applied to each input individually.
+        //    *inputs: arbitrarily nested combination of objects that are compatible with
+        //        shallow_tree. The function `func` is applied to corresponding
+        //        partially flattened elements of each input, so the function must support
+        //        arity of `len(inputs)`.
+
+        //  Raises:
+        //    TypeError: If `shallow_tree` is a sequence but `input_tree` is not.
+        //    TypeError: If the sequence types of `shallow_tree` are different from
+        //      `input_tree`.
+        //    ValueError: If the sequence lengths of `shallow_tree` are different from
+        //      `input_tree`.
+
+        //  Returns:
+        //    result of repeatedly applying `func`, with same structure as
+        //    `shallow_tree`.
+        //  """
+        //  if not inputs:
+        //    raise ValueError("Cannot map over no sequences")
+        //  for input_tree in inputs:
+        //    assert_shallow_structure(shallow_tree, input_tree)
+
+        //# Flatten each input separately, apply the function to corresponding elements,
+        //# then repack based on the structure of the first input.
+        //  all_flattened_up_to = [flatten_up_to(shallow_tree, input_tree)
+        //                         for input_tree in inputs]
+        //  results = [func(*tensors) for tensors in zip(*all_flattened_up_to)]
+        //  return pack_sequence_as(structure=shallow_tree, flat_sequence=results)
+
+
+        //def get_traverse_shallow_structure(traverse_fn, structure):
+        //  """Generates a shallow structure from a `traverse_fn` and `structure`.
+
+        //  `traverse_fn` must accept any possible subtree of `structure` and return
+        //  a depth=1 structure containing `True` or `False` values, describing which
+        //  of the top-level subtrees may be traversed.  It may also
+        //  return scalar `True` or `False` "traversal is OK / not OK for all subtrees."
+
+        //  Examples are available in the unit tests (nest_test.py).
+
+        //  Args:
+        //    traverse_fn: Function taking a substructure and returning either a scalar
+        //      `bool` (whether to traverse that substructure or not) or a depth=1
+        //      shallow structure of the same type, describing which parts of the
+        //      substructure to traverse.
+        //    structure: The structure to traverse.
+
+        //  Returns:
+        //    A shallow structure containing python bools, which can be passed to
+        //    `map_structure_up_to` and `flatten_up_to`.
+
+        //  Raises:
+        //    TypeError: if `traverse_fn` returns a sequence for a non-sequence input,
+        //      or a structure with depth higher than 1 for a sequence input,
+        //      or if any leaf values in the returned structure or scalar are not type
+        //      `bool`.
+        //  """
+        //  to_traverse = traverse_fn(structure)
+        //  if not is_sequence(structure):
+        //    if not isinstance(to_traverse, bool):
+        //      raise TypeError("traverse_fn returned structure: %s for non-structure: %s"
+        //                      % (to_traverse, structure))
+        //    return to_traverse
+        //  level_traverse = []
+        //  if isinstance(to_traverse, bool):
+        //    if not to_traverse:
+        //# Do not traverse this substructure at all.  Exit early.
+        //      return False
+        //    else:
+        //# Traverse the entire substructure.
+        //      for branch in _yield_value(structure):
+        //        level_traverse.append(
+        //            get_traverse_shallow_structure(traverse_fn, branch))
+        //  elif not is_sequence(to_traverse):
+        //    raise TypeError("traverse_fn returned a non-bool scalar: %s for input: %s"
+        //                    % (to_traverse, structure))
+        //  else:
+        //# Traverse some subset of this substructure.
+        //    assert_shallow_structure(to_traverse, structure)
+        //    for t, branch in zip(_yield_value(to_traverse), _yield_value(structure)):
+        //      if not isinstance(t, bool):
+        //        raise TypeError(
+        //            "traverse_fn didn't return a depth=1 structure of bools.  saw: %s "
+        //            " for structure: %s" % (to_traverse, structure))
+        //      if t:
+        //        level_traverse.append(
+        //            get_traverse_shallow_structure(traverse_fn, branch))
+        //      else:
+        //        level_traverse.append(False)
+        //  return _sequence_like(structure, level_traverse)
+
+
+        //def yield_flat_paths(nest):
+        //  """Yields paths for some nested structure.
+
+        //  Paths are lists of objects which can be str-converted, which may include
+        //  integers or other types which are used as indices in a dict.
+
+        //  The flat list will be in the corresponding order as if you called
+        //  `snt.nest.flatten` on the structure. This is handy for naming Tensors such
+        //  the TF scope structure matches the tuple structure.
+
+        //  E.g. if we have a tuple `value = Foo(a=3, b=Bar(c=23, d=42))`
+
+        //  ```shell
+        //  >>> nest.flatten(value)
+        //  [3, 23, 42]
+        //  >>> list(nest.yield_flat_paths(value))
+        //  [('a',), ('b', 'c'), ('b', 'd')]
+        //  ```
+
+        //  ```shell
+        //  >>> list(nest.yield_flat_paths({'a': [3]}))
+        //  [('a', 0)]
+        //  >>> list(nest.yield_flat_paths({'a': 3}))
+        //  [('a',)]
+        //  ```
+
+        //  Args:
+        //    nest: the value to produce a flattened paths list for.
+
+        //  Yields:
+        //    Tuples containing index or key values which form the path to a specific
+        //      leaf value in the nested structure.
+        //  """
+
+        //# The _maybe_add_final_path_element function is used below in order to avoid
+        //# adding trailing slashes when the sub-element recursed into is a leaf.
+        //  if isinstance(nest, (dict, _collections.Mapping)):
+        //    for key in _sorted(nest):
+        //      value = nest[key]
+        //      for sub_path in yield_flat_paths(value):
+        //        yield (key,) + sub_path
+        //  elif _is_namedtuple(nest):
+        //    for key in nest._fields:
+        //      value = getattr(nest, key)
+        //      for sub_path in yield_flat_paths(value):
+        //        yield (key,) + sub_path
+        //  elif isinstance(nest, _six.string_types):
+        //    yield ()
+        //  elif isinstance(nest, _collections.Sequence):
+        //    for idx, value in enumerate(nest):
+        //      for sub_path in yield_flat_paths(value):
+        //        yield (idx,) + sub_path
+        //  else:
+        //    yield ()
+
+
+        //def flatten_with_joined_string_paths(structure, separator="/"):
+        //  """Returns a list of (string path, data element) tuples.
+
+        //  The order of tuples produced matches that of `nest.flatten`. This allows you
+        //  to flatten a nested structure while keeping information about where in the
+        //  structure each data element was located. See `nest.yield_flat_paths`
+        //  for more information.
+
+        //  Args:
+        //    structure: the nested structure to flatten.
+        //    separator: string to separate levels of hierarchy in the results, defaults
+        //      to '/'.
+
+        //  Returns:
+        //    A list of (string, data element) tuples.
+        //  """
+        //  flat_paths = yield_flat_paths(structure)
+        //  def stringify_and_join(path_elements):
+        //    return separator.join(str(path_element) for path_element in path_elements)
+        //  flat_string_paths = [stringify_and_join(path) for path in flat_paths]
+        //  return list(zip(flat_string_paths, flatten(structure)))
+
+
+    }
+}

test/TensorFlowNET.UnitTest/nest_test/NestTest.cs

@@ -0,0 +1,852 @@
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Newtonsoft.Json.Linq;
+using Tensorflow;
+using Tensorflow.Util;
+
+namespace TensorFlowNET.UnitTest.control_flow_ops_test
+{
+    /// <summary>
+    /// excerpt of tensorflow/python/framework/util/nest_test.py
+    /// </summary>
+    [TestClass]
+    public class NestTest : PythonTest
+    {
+
+        public class PointXY
+        {
+            public double x;
+            public double y;
+        }
+
+        //  if attr:
+        //    class BadAttr(object):
+        //      """Class that has a non-iterable __attrs_attrs__."""
+        //      __attrs_attrs__ = None
+
+        //    @attr.s
+        //    class SampleAttr(object):
+        //      field1 = attr.ib()
+        //      field2 = attr.ib()
+
+        //  @test_util.assert_no_new_pyobjects_executing_eagerly
+        //  def testAttrsFlattenAndPack(self) :
+        //    if attr is None:
+        //      self.skipTest("attr module is unavailable.")
+
+        //    field_values = [1, 2]
+        //        sample_attr = NestTest.SampleAttr(* field_values)
+        //        self.assertFalse(nest._is_attrs(field_values))
+        //    self.assertTrue(nest._is_attrs(sample_attr))
+        //    flat = nest.flatten(sample_attr)
+        //    self.assertEqual(field_values, flat)
+        //    restructured_from_flat = nest.pack_sequence_as(sample_attr, flat)
+        //    self.assertIsInstance(restructured_from_flat, NestTest.SampleAttr)
+        //    self.assertEqual(restructured_from_flat, sample_attr)
+
+        //# Check that flatten fails if attributes are not iterable
+        //    with self.assertRaisesRegexp(TypeError, "object is not iterable"):
+        //      flat = nest.flatten(NestTest.BadAttr())
+
+        [TestMethod]
+        public void testFlattenAndPack()
+        {
+            object structure = new object[] {new object[] {3, 4}, 5, new object[] {6, 7, new object[] {9, 10}, 8}};
+            var flat = new List<object> {"a", "b", "c", "d", "e", "f", "g", "h"};
+
+            self.assertEqual(nest.flatten(structure), new[] {3, 4, 5, 6, 7, 9, 10, 8});
+            self.assertEqual(JArray.FromObject(nest.pack_sequence_as(structure, flat)).ToString(),
+                JArray.FromObject(new object[] {new object[] {"a", "b"}, "c", new object[] {"d", "e", new object[] {"f", "g"}, "h"}}).ToString());
+            structure = new object[] { new Hashtable {["x"] = 4, ["y"] = 2}, new object[] { new object[] { new Hashtable { ["x"] = 1,["y"]  = 0}, }, }};
+            flat = new List<object> { 4, 2, 1, 0};
+            self.assertEqual(nest.flatten(structure), flat);
+            //    restructured_from_flat = nest.pack_sequence_as(structure, flat)
+            //    self.assertEqual(restructured_from_flat, structure)
+            //    self.assertEqual(restructured_from_flat[0].x, 4)
+            //    self.assertEqual(restructured_from_flat[0].y, 2)
+            //    self.assertEqual(restructured_from_flat[1][0][0].x, 1)
+            //    self.assertEqual(restructured_from_flat[1][0][0].y, 0)
+
+            //    self.assertEqual([5], nest.flatten(5))
+            //    self.assertEqual([np.array([5])], nest.flatten(np.array([5])))
+
+            //    self.assertEqual("a", nest.pack_sequence_as(5, ["a"]))
+            //    self.assertEqual(
+            //        np.array([5]), nest.pack_sequence_as("scalar", [np.array([5])]))
+
+            //    with self.assertRaisesRegexp(ValueError, "Structure is a scalar"):
+            //      nest.pack_sequence_as("scalar", [4, 5])
+
+            //    with self.assertRaisesRegexp(TypeError, "flat_sequence"):
+            //      nest.pack_sequence_as([4, 5], "bad_sequence")
+
+            //    with self.assertRaises(ValueError):
+            //      nest.pack_sequence_as([5, 6, [7, 8]], ["a", "b", "c"])
+
+        }
+
+        //  @parameterized.parameters({"mapping_type": collections.OrderedDict
+        //    },
+        //                            {"mapping_type": _CustomMapping
+        //})
+        //  @test_util.assert_no_new_pyobjects_executing_eagerly
+        //  def testFlattenDictOrder(self, mapping_type) :
+        //    """`flatten` orders dicts by key, including OrderedDicts."""
+        //    ordered = mapping_type([("d", 3), ("b", 1), ("a", 0), ("c", 2)])
+        //    plain = {"d": 3, "b": 1, "a": 0, "c": 2}
+        //    ordered_flat = nest.flatten(ordered)
+        //    plain_flat = nest.flatten(plain)
+        //    self.assertEqual([0, 1, 2, 3], ordered_flat)
+        //    self.assertEqual([0, 1, 2, 3], plain_flat)
+
+        //  @parameterized.parameters({"mapping_type": collections.OrderedDict},
+        //                            {"mapping_type": _CustomMapping})
+        //  def testPackDictOrder(self, mapping_type):
+        //    """Packing orders dicts by key, including OrderedDicts."""
+        //    custom = mapping_type([("d", 0), ("b", 0), ("a", 0), ("c", 0)])
+        //    plain = {"d": 0, "b": 0, "a": 0, "c": 0}
+        //    seq = [0, 1, 2, 3]
+        //custom_reconstruction = nest.pack_sequence_as(custom, seq)
+        //plain_reconstruction = nest.pack_sequence_as(plain, seq)
+        //    self.assertIsInstance(custom_reconstruction, mapping_type)
+        //    self.assertIsInstance(plain_reconstruction, dict)
+        //    self.assertEqual(
+        //        mapping_type([("d", 3), ("b", 1), ("a", 0), ("c", 2)]),
+        //        custom_reconstruction)
+        //    self.assertEqual({"d": 3, "b": 1, "a": 0, "c": 2}, plain_reconstruction)
+
+        //  Abc = collections.namedtuple("A", ("b", "c"))  # pylint: disable=invalid-name
+
+        //  @test_util.assert_no_new_pyobjects_executing_eagerly
+        //  def testFlattenAndPack_withDicts(self) :
+        //    # A nice messy mix of tuples, lists, dicts, and `OrderedDict`s.
+        //    mess = [
+        //        "z",
+        //        NestTest.Abc(3, 4), {
+        //            "d": _CustomMapping({
+        //                41: 4
+        //            }),
+        //            "c": [
+        //                1,
+        //                collections.OrderedDict([
+        //                    ("b", 3),
+        //                    ("a", 2),
+        //                ]),
+        //            ],
+        //            "b": 5
+        //        }, 17
+        //    ]
+
+        //    flattened = nest.flatten(mess)
+        //    self.assertEqual(flattened, ["z", 3, 4, 5, 1, 2, 3, 4, 17])
+
+        //    structure_of_mess = [
+        //        14,
+        //        NestTest.Abc("a", True),
+        //        {
+        //            "d": _CustomMapping({
+        //                41: 42
+        //            }),
+        //            "c": [
+        //                0,
+        //                collections.OrderedDict([
+        //                    ("b", 9),
+        //                    ("a", 8),
+        //                ]),
+        //            ],
+        //            "b": 3
+        //        },
+        //        "hi everybody",
+        //    ]
+
+        //    unflattened = nest.pack_sequence_as(structure_of_mess, flattened)
+        //    self.assertEqual(unflattened, mess)
+
+        //    # Check also that the OrderedDict was created, with the correct key order.
+        //unflattened_ordered_dict = unflattened[2]["c"][1]
+        //    self.assertIsInstance(unflattened_ordered_dict, collections.OrderedDict)
+        //    self.assertEqual(list(unflattened_ordered_dict.keys()), ["b", "a"])
+
+        //    unflattened_custom_mapping = unflattened[2]["d"]
+        //    self.assertIsInstance(unflattened_custom_mapping, _CustomMapping)
+        //    self.assertEqual(list(unflattened_custom_mapping.keys()), [41])
+
+        //  def testFlatten_numpyIsNotFlattened(self):
+        //    structure = np.array([1, 2, 3])
+        //    flattened = nest.flatten(structure)
+        //    self.assertEqual(len(flattened), 1)
+
+        //  def testFlatten_stringIsNotFlattened(self):
+        //    structure = "lots of letters"
+        //    flattened = nest.flatten(structure)
+        //    self.assertEqual(len(flattened), 1)
+        //    unflattened = nest.pack_sequence_as("goodbye", flattened)
+        //    self.assertEqual(structure, unflattened)
+
+        //  def testPackSequenceAs_notIterableError(self) :
+        //    with self.assertRaisesRegexp(TypeError,
+        //                                 "flat_sequence must be a sequence"):
+        //      nest.pack_sequence_as("hi", "bye")
+
+        //  def testPackSequenceAs_wrongLengthsError(self):
+        //    with self.assertRaisesRegexp(
+        //        ValueError,
+        //        "Structure had 2 elements, but flat_sequence had 3 elements."):
+        //      nest.pack_sequence_as(["hello", "world"],
+        //                            ["and", "goodbye", "again"])
+
+        //  @test_util.assert_no_new_pyobjects_executing_eagerly
+        //  def testIsSequence(self):
+        //    self.assertFalse(nest.is_sequence("1234"))
+        //    self.assertTrue(nest.is_sequence([1, 3, [4, 5]]))
+        //    self.assertTrue(nest.is_sequence(((7, 8), (5, 6))))
+        //    self.assertTrue(nest.is_sequence([]))
+        //    self.assertTrue(nest.is_sequence({"a": 1, "b": 2}))
+        //    self.assertFalse(nest.is_sequence(set([1, 2])))
+        //    ones = array_ops.ones([2, 3])
+        //    self.assertFalse(nest.is_sequence(ones))
+        //    self.assertFalse(nest.is_sequence(math_ops.tanh(ones)))
+        //    self.assertFalse(nest.is_sequence(np.ones((4, 5))))
+
+        //  @parameterized.parameters({"mapping_type": _CustomMapping},
+        //                            {"mapping_type": dict})
+        //  def testFlattenDictItems(self, mapping_type):
+        //    dictionary = mapping_type({ (4, 5, (6, 8)): ("a", "b", ("c", "d"))})
+        //    flat = {4: "a", 5: "b", 6: "c", 8: "d"}
+        //    self.assertEqual(nest.flatten_dict_items(dictionary), flat)
+
+        //    with self.assertRaises(TypeError):
+        //      nest.flatten_dict_items(4)
+
+        //    bad_dictionary = mapping_type({ (4, 5, (4, 8)): ("a", "b", ("c", "d"))})
+        //    with self.assertRaisesRegexp(ValueError, "not unique"):
+        //      nest.flatten_dict_items(bad_dictionary)
+
+        //    another_bad_dictionary = mapping_type({
+        //        (4, 5, (6, 8)): ("a", "b", ("c", ("d", "e")))
+        //    })
+        //    with self.assertRaisesRegexp(
+        //        ValueError, "Key had [0-9]* elements, but value had [0-9]* elements"):
+        //      nest.flatten_dict_items(another_bad_dictionary)
+
+        //# pylint does not correctly recognize these as class names and
+        //# suggests to use variable style under_score naming.
+        //# pylint: disable=invalid-name
+        //  Named0ab = collections.namedtuple("named_0", ("a", "b"))
+        //  Named1ab = collections.namedtuple("named_1", ("a", "b"))
+        //  SameNameab = collections.namedtuple("same_name", ("a", "b"))
+        //  SameNameab2 = collections.namedtuple("same_name", ("a", "b"))
+        //  SameNamexy = collections.namedtuple("same_name", ("x", "y"))
+        //  SameName1xy = collections.namedtuple("same_name_1", ("x", "y"))
+        //  SameName1xy2 = collections.namedtuple("same_name_1", ("x", "y"))
+        //  NotSameName = collections.namedtuple("not_same_name", ("a", "b"))
+        //  # pylint: enable=invalid-name
+
+        //  class SameNamedType1(SameNameab):
+        //    pass
+
+        //  @test_util.assert_no_new_pyobjects_executing_eagerly
+        //  def testAssertSameStructure(self):
+        //    structure1 = (((1, 2), 3), 4, (5, 6))
+        //    structure2 = ((("foo1", "foo2"), "foo3"), "foo4", ("foo5", "foo6"))
+        //    structure_different_num_elements = ("spam", "eggs")
+        //    structure_different_nesting = (((1, 2), 3), 4, 5, (6,))
+        //    nest.assert_same_structure(structure1, structure2)
+        //    nest.assert_same_structure("abc", 1.0)
+        //    nest.assert_same_structure("abc", np.array([0, 1]))
+        //    nest.assert_same_structure("abc", constant_op.constant([0, 1]))
+
+        //    with self.assertRaisesRegexp(
+        //        ValueError,
+        //        ("The two structures don't have the same nested structure\\.\n\n"
+        //         "First structure:.*?\n\n"
+        //         "Second structure:.*\n\n"
+        //         "More specifically: Substructure "
+        //         r'"type=tuple str=\(\(1, 2\), 3\)" is a sequence, while '
+        //         'substructure "type=str str=spam" is not\n'
+        //         "Entire first structure:\n"
+        //         r"\(\(\(\., \.\), \.\), \., \(\., \.\)\)\n"
+        //         "Entire second structure:\n"
+        //         r"\(\., \.\)")):
+        //      nest.assert_same_structure(structure1, structure_different_num_elements)
+
+        //    with self.assertRaisesRegexp(
+        //        ValueError,
+        //        ("The two structures don't have the same nested structure\\.\n\n"
+        //         "First structure:.*?\n\n"
+        //         "Second structure:.*\n\n"
+        //         r'More specifically: Substructure "type=list str=\[0, 1\]" '
+        //         r'is a sequence, while substructure "type=ndarray str=\[0 1\]" '
+        //         "is not")):
+        //      nest.assert_same_structure([0, 1], np.array([0, 1]))
+
+        //    with self.assertRaisesRegexp(
+        //        ValueError,
+        //        ("The two structures don't have the same nested structure\\.\n\n"
+        //         "First structure:.*?\n\n"
+        //         "Second structure:.*\n\n"
+        //         r'More specifically: Substructure "type=list str=\[0, 1\]" '
+        //         'is a sequence, while substructure "type=int str=0" '
+        //         "is not")):
+        //      nest.assert_same_structure(0, [0, 1])
+
+        //    self.assertRaises(TypeError, nest.assert_same_structure, (0, 1), [0, 1])
+
+        //    with self.assertRaisesRegexp(
+        //        ValueError,
+        //        ("don't have the same nested structure\\.\n\n"
+        //         "First structure: .*?\n\nSecond structure: ")):
+        //      nest.assert_same_structure(structure1, structure_different_nesting)
+
+        //    self.assertRaises(TypeError, nest.assert_same_structure, (0, 1),
+        //                      NestTest.Named0ab("a", "b"))
+
+        //    nest.assert_same_structure(NestTest.Named0ab(3, 4),
+        //                               NestTest.Named0ab("a", "b"))
+
+        //    self.assertRaises(TypeError, nest.assert_same_structure,
+        //                      NestTest.Named0ab(3, 4), NestTest.Named1ab(3, 4))
+
+        //    with self.assertRaisesRegexp(
+        //        ValueError,
+        //        ("don't have the same nested structure\\.\n\n"
+        //         "First structure: .*?\n\nSecond structure: ")):
+        //      nest.assert_same_structure(NestTest.Named0ab(3, 4),
+        //                                 NestTest.Named0ab([3], 4))
+
+        //    with self.assertRaisesRegexp(
+        //        ValueError,
+        //        ("don't have the same nested structure\\.\n\n"
+        //         "First structure: .*?\n\nSecond structure: ")):
+        //      nest.assert_same_structure([[3], 4], [3, [4]])
+
+        //    structure1_list = [[[1, 2], 3], 4, [5, 6]]
+        //    with self.assertRaisesRegexp(TypeError,
+        //                                 "don't have the same sequence type"):
+        //      nest.assert_same_structure(structure1, structure1_list)
+        //    nest.assert_same_structure(structure1, structure2, check_types= False)
+        //    nest.assert_same_structure(structure1, structure1_list, check_types=False)
+
+        //    with self.assertRaisesRegexp(ValueError,
+        //                                 "don't have the same set of keys"):
+        //      nest.assert_same_structure({"a": 1}, {"b": 1})
+
+        //    nest.assert_same_structure(NestTest.SameNameab(0, 1),
+        //                               NestTest.SameNameab2(2, 3))
+
+        //    # This assertion is expected to pass: two namedtuples with the same
+        //    # name and field names are considered to be identical.
+        //    nest.assert_same_structure(
+        //        NestTest.SameNameab(NestTest.SameName1xy(0, 1), 2),
+        //        NestTest.SameNameab2(NestTest.SameName1xy2(2, 3), 4))
+
+        //    expected_message = "The two structures don't have the same.*"
+        //    with self.assertRaisesRegexp(ValueError, expected_message):
+        //      nest.assert_same_structure(
+        //          NestTest.SameNameab(0, NestTest.SameNameab2(1, 2)),
+        //          NestTest.SameNameab2(NestTest.SameNameab(0, 1), 2))
+
+        //    self.assertRaises(TypeError, nest.assert_same_structure,
+        //                      NestTest.SameNameab(0, 1), NestTest.NotSameName(2, 3))
+
+        //    self.assertRaises(TypeError, nest.assert_same_structure,
+        //                      NestTest.SameNameab(0, 1), NestTest.SameNamexy(2, 3))
+
+        //    self.assertRaises(TypeError, nest.assert_same_structure,
+        //                      NestTest.SameNameab(0, 1), NestTest.SameNamedType1(2, 3))
+
+        //  EmptyNT = collections.namedtuple("empty_nt", "")  # pylint: disable=invalid-name
+
+        //  def testHeterogeneousComparison(self):
+        //    nest.assert_same_structure({"a": 4}, _CustomMapping(a= 3))
+        //    nest.assert_same_structure(_CustomMapping(b=3), {"b": 4})
+
+        //  @test_util.assert_no_new_pyobjects_executing_eagerly
+        //  def testMapStructure(self) :
+        //    structure1 = (((1, 2), 3), 4, (5, 6))
+        //    structure2 = (((7, 8), 9), 10, (11, 12))
+        //    structure1_plus1 = nest.map_structure(lambda x: x + 1, structure1)
+        //    nest.assert_same_structure(structure1, structure1_plus1)
+        //    self.assertAllEqual(
+        //        [2, 3, 4, 5, 6, 7],
+        //        nest.flatten(structure1_plus1))
+        //    structure1_plus_structure2 = nest.map_structure(
+        //        lambda x, y: x + y, structure1, structure2)
+        //    self.assertEqual(
+        //        (((1 + 7, 2 + 8), 3 + 9), 4 + 10, (5 + 11, 6 + 12)),
+        //        structure1_plus_structure2)
+
+        //    self.assertEqual(3, nest.map_structure(lambda x: x - 1, 4))
+
+        //    self.assertEqual(7, nest.map_structure(lambda x, y: x + y, 3, 4))
+
+        //    # Empty structures
+        //    self.assertEqual((), nest.map_structure(lambda x: x + 1, ()))
+        //    self.assertEqual([], nest.map_structure(lambda x: x + 1, []))
+        //    self.assertEqual({}, nest.map_structure(lambda x: x + 1, {}))
+        //    self.assertEqual(NestTest.EmptyNT(), nest.map_structure(lambda x: x + 1,
+        //                                                            NestTest.EmptyNT()))
+
+        //    # This is checking actual equality of types, empty list != empty tuple
+        //    self.assertNotEqual((), nest.map_structure(lambda x: x + 1, []))
+
+        //    with self.assertRaisesRegexp(TypeError, "callable"):
+        //      nest.map_structure("bad", structure1_plus1)
+
+        //    with self.assertRaisesRegexp(ValueError, "at least one structure"):
+        //      nest.map_structure(lambda x: x)
+
+        //    with self.assertRaisesRegexp(ValueError, "same number of elements"):
+        //      nest.map_structure(lambda x, y: None, (3, 4), (3, 4, 5))
+
+        //    with self.assertRaisesRegexp(ValueError, "same nested structure"):
+        //      nest.map_structure(lambda x, y: None, 3, (3,))
+
+        //    with self.assertRaisesRegexp(TypeError, "same sequence type"):
+        //      nest.map_structure(lambda x, y: None, ((3, 4), 5), [(3, 4), 5])
+
+        //    with self.assertRaisesRegexp(ValueError, "same nested structure"):
+        //      nest.map_structure(lambda x, y: None, ((3, 4), 5), (3, (4, 5)))
+
+        //    structure1_list = [[[1, 2], 3], 4, [5, 6]]
+        //    with self.assertRaisesRegexp(TypeError, "same sequence type"):
+        //      nest.map_structure(lambda x, y: None, structure1, structure1_list)
+
+        //    nest.map_structure(lambda x, y: None, structure1, structure1_list,
+        //                       check_types=False)
+
+        //    with self.assertRaisesRegexp(ValueError, "same nested structure"):
+        //      nest.map_structure(lambda x, y: None, ((3, 4), 5), (3, (4, 5)),
+        //                         check_types=False)
+
+        //    with self.assertRaisesRegexp(ValueError, "Only valid keyword argument"):
+        //      nest.map_structure(lambda x: None, structure1, foo="a")
+
+        //    with self.assertRaisesRegexp(ValueError, "Only valid keyword argument"):
+        //      nest.map_structure(lambda x: None, structure1, check_types=False, foo="a")
+
+        //  ABTuple = collections.namedtuple("ab_tuple", "a, b")  # pylint: disable=invalid-name
+
+        //  @test_util.assert_no_new_pyobjects_executing_eagerly
+        //  def testMapStructureWithStrings(self) :
+        //    inp_a = NestTest.ABTuple(a="foo", b=("bar", "baz"))
+        //    inp_b = NestTest.ABTuple(a=2, b=(1, 3))
+        //    out = nest.map_structure(lambda string, repeats: string* repeats,
+        //                             inp_a,
+        //                             inp_b)
+        //    self.assertEqual("foofoo", out.a)
+        //    self.assertEqual("bar", out.b[0])
+        //    self.assertEqual("bazbazbaz", out.b[1])
+
+        //    nt = NestTest.ABTuple(a=("something", "something_else"),
+        //                          b="yet another thing")
+        //    rev_nt = nest.map_structure(lambda x: x[::- 1], nt)
+        //    # Check the output is the correct structure, and all strings are reversed.
+        //    nest.assert_same_structure(nt, rev_nt)
+        //    self.assertEqual(nt.a[0][::- 1], rev_nt.a[0])
+        //    self.assertEqual(nt.a[1][::- 1], rev_nt.a[1])
+        //    self.assertEqual(nt.b[::- 1], rev_nt.b)
+
+        //  @test_util.run_deprecated_v1
+        //  def testMapStructureOverPlaceholders(self) :
+        //    inp_a = (array_ops.placeholder(dtypes.float32, shape=[3, 4]),
+        //             array_ops.placeholder(dtypes.float32, shape=[3, 7]))
+        //    inp_b = (array_ops.placeholder(dtypes.float32, shape=[3, 4]),
+        //             array_ops.placeholder(dtypes.float32, shape=[3, 7]))
+
+        //    output = nest.map_structure(lambda x1, x2: x1 + x2, inp_a, inp_b)
+
+        //    nest.assert_same_structure(output, inp_a)
+        //    self.assertShapeEqual(np.zeros((3, 4)), output[0])
+        //    self.assertShapeEqual(np.zeros((3, 7)), output[1])
+
+        //    feed_dict = {
+        //        inp_a: (np.random.randn(3, 4), np.random.randn(3, 7)),
+        //        inp_b: (np.random.randn(3, 4), np.random.randn(3, 7))
+        //    }
+
+        //    with self.cached_session() as sess:
+        //      output_np = sess.run(output, feed_dict=feed_dict)
+        //    self.assertAllClose(output_np[0],
+        //                        feed_dict[inp_a][0] + feed_dict[inp_b][0])
+        //    self.assertAllClose(output_np[1],
+        //                        feed_dict[inp_a][1] + feed_dict[inp_b][1])
+
+        //  def testAssertShallowStructure(self):
+        //    inp_ab = ["a", "b"]
+        //inp_abc = ["a", "b", "c"]
+        //expected_message = (
+        //        "The two structures don't have the same sequence length. Input "
+        //        "structure has length 2, while shallow structure has length 3.")
+        //    with self.assertRaisesRegexp(ValueError, expected_message):
+        //      nest.assert_shallow_structure(inp_abc, inp_ab)
+
+        //    inp_ab1 = [(1, 1), (2, 2)]
+        //    inp_ab2 = [[1, 1], [2, 2]]
+        //    expected_message = (
+        //        "The two structures don't have the same sequence type. Input structure "
+        //        "has type <(type|class) 'tuple'>, while shallow structure has type "
+        //        "<(type|class) 'list'>.")
+        //    with self.assertRaisesRegexp(TypeError, expected_message):
+        //      nest.assert_shallow_structure(inp_ab2, inp_ab1)
+        //    nest.assert_shallow_structure(inp_ab2, inp_ab1, check_types= False)
+
+        //    inp_ab1 = {"a": (1, 1), "b": {"c": (2, 2)}}
+        //    inp_ab2 = {"a": (1, 1), "b": {"d": (2, 2)}}
+        //    expected_message = (
+        //        r"The two structures don't have the same keys. Input "
+        //        r"structure has keys \['c'\], while shallow structure has "
+        //        r"keys \['d'\].")
+
+        //    with self.assertRaisesRegexp(ValueError, expected_message):
+        //      nest.assert_shallow_structure(inp_ab2, inp_ab1)
+
+        //    inp_ab = collections.OrderedDict([("a", 1), ("b", (2, 3))])
+        //    inp_ba = collections.OrderedDict([("b", (2, 3)), ("a", 1)])
+        //    nest.assert_shallow_structure(inp_ab, inp_ba)
+
+        //    # This assertion is expected to pass: two namedtuples with the same
+        //# name and field names are considered to be identical.
+        //inp_shallow = NestTest.SameNameab(1, 2)
+        //    inp_deep = NestTest.SameNameab2(1, [1, 2, 3])
+        //    nest.assert_shallow_structure(inp_shallow, inp_deep, check_types=False)
+        //    nest.assert_shallow_structure(inp_shallow, inp_deep, check_types=True)
+
+        //  def testFlattenUpTo(self):
+        //    # Shallow tree ends at scalar.
+        //    input_tree = [[[2, 2], [3, 3]], [[4, 9], [5, 5]]]
+        //    shallow_tree = [[True, True], [False, True]]
+        //    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_input_tree, [[2, 2], [3, 3], [4, 9], [5, 5]])
+        //    self.assertEqual(flattened_shallow_tree, [True, True, False, True])
+
+        //# Shallow tree ends at string.
+        //    input_tree = [[("a", 1), [("b", 2), [("c", 3), [("d", 4)]]]]]
+        //    shallow_tree = [["level_1", ["level_2", ["level_3", ["level_4"]]]]]
+        //    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+        //                                                              input_tree)
+        //    input_tree_flattened = nest.flatten(input_tree)
+        //    self.assertEqual(input_tree_flattened_as_shallow_tree,
+        //                     [("a", 1), ("b", 2), ("c", 3), ("d", 4)])
+        //    self.assertEqual(input_tree_flattened, ["a", 1, "b", 2, "c", 3, "d", 4])
+
+        //    # Make sure dicts are correctly flattened, yielding values, not keys.
+        //input_tree = {"a": 1, "b": {"c": 2}, "d": [3, (4, 5)]}
+        //    shallow_tree = {"a": 0, "b": 0, "d": [0, 0]}
+        //    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+        //                                                              input_tree)
+        //    self.assertEqual(input_tree_flattened_as_shallow_tree,
+        //                     [1, { "c": 2}, 3, (4, 5)])
+
+        //    # Namedtuples.
+        //    ab_tuple = NestTest.ABTuple
+        //    input_tree = ab_tuple(a =[0, 1], b = 2)
+        //    shallow_tree = ab_tuple(a= 0, b= 1)
+        //    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+        //                                                              input_tree)
+        //    self.assertEqual(input_tree_flattened_as_shallow_tree,
+        //                     [[0, 1], 2])
+
+        //    # Nested dicts, OrderedDicts and namedtuples.
+        //    input_tree = collections.OrderedDict(
+        //        [("a", ab_tuple(a =[0, {"b": 1}], b=2)),
+        //         ("c", {"d": 3, "e": collections.OrderedDict([("f", 4)])})])
+        //    shallow_tree = input_tree
+        //    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+        //                                                              input_tree)
+        //    self.assertEqual(input_tree_flattened_as_shallow_tree, [0, 1, 2, 3, 4])
+        //    shallow_tree = collections.OrderedDict([("a", 0), ("c", {"d": 3, "e": 1})])
+        //    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+        //                                                              input_tree)
+        //    self.assertEqual(input_tree_flattened_as_shallow_tree,
+        //                     [ab_tuple(a =[0, { "b": 1}], b=2),
+        //                      3,
+        //                      collections.OrderedDict([("f", 4)])])
+        //    shallow_tree = collections.OrderedDict([("a", 0), ("c", 0)])
+        //    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+        //                                                              input_tree)
+        //    self.assertEqual(input_tree_flattened_as_shallow_tree,
+        //                     [ab_tuple(a =[0, {"b": 1}], b=2),
+        //                      {"d": 3, "e": collections.OrderedDict([("f", 4)])}])
+
+        //    ## Shallow non-list edge-case.
+        //    # Using iterable elements.
+        //    input_tree = ["input_tree"]
+        //shallow_tree = "shallow_tree"
+        //    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_input_tree, [input_tree])
+        //    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+        //    input_tree = ["input_tree_0", "input_tree_1"]
+        //shallow_tree = "shallow_tree"
+        //    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_input_tree, [input_tree])
+        //    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+        //    # Using non-iterable elements.
+        //input_tree = [0]
+        //shallow_tree = 9
+        //    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_input_tree, [input_tree])
+        //    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+        //    input_tree = [0, 1]
+        //shallow_tree = 9
+        //    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_input_tree, [input_tree])
+        //    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+        //    ## Both non-list edge-case.
+        //# Using iterable elements.
+        //input_tree = "input_tree"
+        //    shallow_tree = "shallow_tree"
+        //    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_input_tree, [input_tree])
+        //    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+        //    # Using non-iterable elements.
+        //input_tree = 0
+        //    shallow_tree = 0
+        //    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_input_tree, [input_tree])
+        //    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+        //    ## Input non-list edge-case.
+        //# Using iterable elements.
+        //input_tree = "input_tree"
+        //    shallow_tree = ["shallow_tree"]
+        //expected_message = ("If shallow structure is a sequence, input must also "
+        //                        "be a sequence. Input has type: <(type|class) 'str'>.")
+        //    with self.assertRaisesRegexp(TypeError, expected_message):
+        //      flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_shallow_tree, shallow_tree)
+
+        //    input_tree = "input_tree"
+        //    shallow_tree = ["shallow_tree_9", "shallow_tree_8"]
+        //with self.assertRaisesRegexp(TypeError, expected_message):
+        //      flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_shallow_tree, shallow_tree)
+
+        //# Using non-iterable elements.
+        //    input_tree = 0
+        //    shallow_tree = [9]
+        //expected_message = ("If shallow structure is a sequence, input must also "
+        //                        "be a sequence. Input has type: <(type|class) 'int'>.")
+        //    with self.assertRaisesRegexp(TypeError, expected_message):
+        //      flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_shallow_tree, shallow_tree)
+
+        //    input_tree = 0
+        //    shallow_tree = [9, 8]
+        //with self.assertRaisesRegexp(TypeError, expected_message):
+        //      flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+        //    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+        //    self.assertEqual(flattened_shallow_tree, shallow_tree)
+
+        //  def testMapStructureUpTo(self) :
+        //    # Named tuples.
+        //    ab_tuple = collections.namedtuple("ab_tuple", "a, b")
+        //    op_tuple = collections.namedtuple("op_tuple", "add, mul")
+        //    inp_val = ab_tuple(a= 2, b= 3)
+        //    inp_ops = ab_tuple(a= op_tuple(add = 1, mul = 2), b= op_tuple(add = 2, mul = 3))
+        //    out = nest.map_structure_up_to(
+        //        inp_val, lambda val, ops: (val + ops.add) * ops.mul, inp_val, inp_ops)
+        //    self.assertEqual(out.a, 6)
+        //    self.assertEqual(out.b, 15)
+
+        //    # Lists.
+        //    data_list = [[2, 4, 6, 8], [[1, 3, 5, 7, 9], [3, 5, 7]]]
+        //    name_list = ["evens", ["odds", "primes"]]
+        //    out = nest.map_structure_up_to(
+        //        name_list, lambda name, sec: "first_{}_{}".format(len(sec), name),
+        //        name_list, data_list)
+        //    self.assertEqual(out, ["first_4_evens", ["first_5_odds", "first_3_primes"]])
+
+        //    # Dicts.
+        //    inp_val = dict(a= 2, b= 3)
+        //    inp_ops = dict(a= dict(add = 1, mul = 2), b= dict(add = 2, mul = 3))
+        //    out = nest.map_structure_up_to(
+        //        inp_val,
+        //        lambda val, ops: (val + ops["add"]) * ops["mul"], inp_val, inp_ops)
+        //    self.assertEqual(out["a"], 6)
+        //    self.assertEqual(out["b"], 15)
+
+        //    # Non-equal dicts.
+        //    inp_val = dict(a= 2, b= 3)
+        //    inp_ops = dict(a= dict(add = 1, mul = 2), c= dict(add = 2, mul = 3))
+        //    with self.assertRaisesRegexp(ValueError, "same keys"):
+        //      nest.map_structure_up_to(
+        //          inp_val,
+        //          lambda val, ops: (val + ops["add"]) * ops["mul"], inp_val, inp_ops)
+
+        //    # Dict+custom mapping.
+        //    inp_val = dict(a= 2, b= 3)
+        //    inp_ops = _CustomMapping(a= dict(add = 1, mul = 2), b= dict(add = 2, mul = 3))
+        //    out = nest.map_structure_up_to(
+        //        inp_val,
+        //        lambda val, ops: (val + ops["add"]) * ops["mul"], inp_val, inp_ops)
+        //    self.assertEqual(out["a"], 6)
+        //    self.assertEqual(out["b"], 15)
+
+        //    # Non-equal dict/mapping.
+        //    inp_val = dict(a= 2, b= 3)
+        //    inp_ops = _CustomMapping(a= dict(add = 1, mul = 2), c= dict(add = 2, mul = 3))
+        //    with self.assertRaisesRegexp(ValueError, "same keys"):
+        //      nest.map_structure_up_to(
+        //          inp_val,
+        //          lambda val, ops: (val + ops["add"]) * ops["mul"], inp_val, inp_ops)
+
+        //  def testGetTraverseShallowStructure(self):
+        //    scalar_traverse_input = [3, 4, (1, 2, [0]), [5, 6], {"a": (7,)}, []]
+        //    scalar_traverse_r = nest.get_traverse_shallow_structure(
+        //        lambda s: not isinstance(s, tuple),
+        //        scalar_traverse_input)
+        //    self.assertEqual(scalar_traverse_r,
+        //                     [True, True, False, [True, True], {"a": False}, []])
+        //    nest.assert_shallow_structure(scalar_traverse_r,
+        //                                  scalar_traverse_input)
+
+        //    structure_traverse_input = [(1, [2]), ([1], 2)]
+        //    structure_traverse_r = nest.get_traverse_shallow_structure(
+        //        lambda s: (True, False) if isinstance(s, tuple) else True,
+        //        structure_traverse_input)
+        //    self.assertEqual(structure_traverse_r,
+        //                     [(True, False), ([True], False)])
+        //    nest.assert_shallow_structure(structure_traverse_r,
+        //                                  structure_traverse_input)
+
+        //    with self.assertRaisesRegexp(TypeError, "returned structure"):
+        //      nest.get_traverse_shallow_structure(lambda _: [True], 0)
+
+        //    with self.assertRaisesRegexp(TypeError, "returned a non-bool scalar"):
+        //      nest.get_traverse_shallow_structure(lambda _: 1, [1])
+
+        //    with self.assertRaisesRegexp(
+        //        TypeError, "didn't return a depth=1 structure of bools"):
+        //      nest.get_traverse_shallow_structure(lambda _: [1], [1])
+
+        //  def testYieldFlatStringPaths(self):
+        //    for inputs_expected in ({"inputs": [], "expected": []},
+        //                            {"inputs": 3, "expected": [()]},
+        //                            {"inputs": [3], "expected": [(0,)]},
+        //                            {"inputs": {"a": 3}, "expected": [("a",)]},
+        //                            {"inputs": {"a": {"b": 4}},
+        //                             "expected": [("a", "b")]},
+        //                            {"inputs": [{"a": 2}], "expected": [(0, "a")]},
+        //                            {"inputs": [{"a": [2]}], "expected": [(0, "a", 0)]},
+        //                            {"inputs": [{"a": [(23, 42)]}],
+        //                             "expected": [(0, "a", 0, 0), (0, "a", 0, 1)]},
+        //                            {"inputs": [{"a": ([23], 42)}],
+        //                             "expected": [(0, "a", 0, 0), (0, "a", 1)]},
+        //                            {"inputs": {"a": {"a": 2}, "c": [[[4]]]},
+        //                             "expected": [("a", "a"), ("c", 0, 0, 0)]},
+        //                            {"inputs": {"0": [{"1": 23}]},
+        //                             "expected": [("0", 0, "1")]}):
+        //      inputs = inputs_expected["inputs"]
+        //      expected = inputs_expected["expected"]
+        //      self.assertEqual(list(nest.yield_flat_paths(inputs)), expected)
+
+        //  def testFlattenWithStringPaths(self):
+        //    for inputs_expected in (
+        //        {"inputs": [], "expected": []},
+        //        {"inputs": [23, "42"], "expected": [("0", 23), ("1", "42")]},
+        //        {"inputs": [[[[108]]]], "expected": [("0/0/0/0", 108)]}):
+        //      inputs = inputs_expected["inputs"]
+        //      expected = inputs_expected["expected"]
+        //      self.assertEqual(
+        //          nest.flatten_with_joined_string_paths(inputs, separator="/"),
+        //          expected)
+
+        //  # Need a separate test for namedtuple as we can't declare tuple definitions
+        //  # in the @parameterized arguments.
+        //  def testFlattenNamedTuple(self):
+        //    # pylint: disable=invalid-name
+        //    Foo = collections.namedtuple("Foo", ["a", "b"])
+        //    Bar = collections.namedtuple("Bar", ["c", "d"])
+        //    # pylint: enable=invalid-name
+        //    test_cases = [
+        //        (Foo(a = 3, b = Bar(c = 23, d = 42)),
+        //         [("a", 3), ("b/c", 23), ("b/d", 42)]),
+        //        (Foo(a = Bar(c = 23, d = 42), b = Bar(c = 0, d = "something")),
+        //         [("a/c", 23), ("a/d", 42), ("b/c", 0), ("b/d", "something")]),
+        //        (Bar(c = 42, d = 43),
+        //         [("c", 42), ("d", 43)]),
+        //        (Bar(c =[42], d = 43),
+        //         [("c/0", 42), ("d", 43)]),
+        //    ]
+        //    for inputs, expected in test_cases:
+        //      self.assertEqual(
+        //          list(nest.flatten_with_joined_string_paths(inputs)), expected)
+
+        //  @parameterized.named_parameters(
+        //      ("tuples", (1, 2), (3, 4), True, (("0", 4), ("1", 6))),
+        //      ("dicts", {"a": 1, "b": 2}, {"b": 4, "a": 3}, True,
+        //       {"a": ("a", 4), "b": ("b", 6)}),
+        //      ("mixed", (1, 2), [3, 4], False, (("0", 4), ("1", 6))),
+        //      ("nested",
+        //       {"a": [2, 3], "b": [1, 2, 3]}, {"b": [5, 6, 7], "a": [8, 9]}, True,
+        //       {"a": [("a/0", 10), ("a/1", 12)],
+        //        "b": [("b/0", 6), ("b/1", 8), ("b/2", 10)]}))
+        //  def testMapWithPathsCompatibleStructures(self, s1, s2, check_types, expected):
+        //    def format_sum(path, * values):
+        //      return (path, sum(values))
+        //    result = nest.map_structure_with_paths(format_sum, s1, s2,
+        //                                           check_types=check_types)
+        //    self.assertEqual(expected, result)
+
+        //  @parameterized.named_parameters(
+        //      ("tuples", (1, 2), (3, 4, 5), ValueError),
+        //      ("dicts", {"a": 1}, {"b": 2}, ValueError),
+        //      ("mixed", (1, 2), [3, 4], TypeError),
+        //      ("nested",
+        //       {"a": [2, 3], "b": [1, 3]},
+        //       {"b": [5, 6, 7], "a": [8, 9]},
+        //       ValueError
+        //      ))
+        //  def testMapWithPathsIncompatibleStructures(self, s1, s2, error_type):
+        //    with self.assertRaises(error_type):
+        //      nest.map_structure_with_paths(lambda path, * s: 0, s1, s2)
+
+
+        //class NestBenchmark(test.Benchmark):
+
+        //  def run_and_report(self, s1, s2, name):
+        //    burn_iter, test_iter = 100, 30000
+
+        //    for _ in xrange(burn_iter) :
+        //      nest.assert_same_structure(s1, s2)
+
+        //    t0 = time.time()
+        //    for _ in xrange(test_iter) :
+        //      nest.assert_same_structure(s1, s2)
+        //    t1 = time.time()
+
+        //    self.report_benchmark(iters=test_iter, wall_time=(t1 - t0) / test_iter,
+        //                          name=name)
+
+        //  def benchmark_assert_structure(self):
+        //    s1 = (((1, 2), 3), 4, (5, 6))
+        //    s2 = ((("foo1", "foo2"), "foo3"), "foo4", ("foo5", "foo6"))
+        //    self.run_and_report(s1, s2, "assert_same_structure_6_elem")
+
+        //    s1 = (((1, 2), 3), 4, (5, 6)) * 10
+        //    s2 = ((("foo1", "foo2"), "foo3"), "foo4", ("foo5", "foo6")) * 10
+        //    self.run_and_report(s1, s2, "assert_same_structure_60_elem")
+
+
+        //if __name__ == "__main__":
+        //  test.main()
+    }
+}

test/TensorFlowNET.UnitTest/nest_test/nest_test.py

@@ -0,0 +1,883 @@
+# Copyright 2016 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Tests for utilities working with arbitrarily nested structures."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import collections
+import time
+
+from absl.testing import parameterized
+import numpy as np
+from six.moves import xrange  # pylint: disable=redefined-builtin
+
+from tensorflow.python.framework import constant_op
+from tensorflow.python.framework import dtypes
+from tensorflow.python.framework import test_util
+from tensorflow.python.ops import array_ops
+from tensorflow.python.ops import math_ops
+from tensorflow.python.platform import test
+from tensorflow.python.util import nest
+
+try:
+  import attr  # pylint:disable=g-import-not-at-top
+except ImportError:
+  attr = None
+
+
+class _CustomMapping(collections.Mapping):
+
+  def __init__(self, *args, **kwargs):
+    self._wrapped = dict(*args, **kwargs)
+
+  def __getitem__(self, key):
+    return self._wrapped[key]
+
+  def __iter__(self):
+    return iter(self._wrapped)
+
+  def __len__(self):
+    return len(self._wrapped)
+
+
+class NestTest(parameterized.TestCase, test.TestCase):
+
+  PointXY = collections.namedtuple("Point", ["x", "y"])  # pylint: disable=invalid-name
+
+  if attr:
+    class BadAttr(object):
+      """Class that has a non-iterable __attrs_attrs__."""
+      __attrs_attrs__ = None
+
+    @attr.s
+    class SampleAttr(object):
+      field1 = attr.ib()
+      field2 = attr.ib()
+
+  @test_util.assert_no_new_pyobjects_executing_eagerly
+  def testAttrsFlattenAndPack(self):
+    if attr is None:
+      self.skipTest("attr module is unavailable.")
+
+    field_values = [1, 2]
+    sample_attr = NestTest.SampleAttr(*field_values)
+    self.assertFalse(nest._is_attrs(field_values))
+    self.assertTrue(nest._is_attrs(sample_attr))
+    flat = nest.flatten(sample_attr)
+    self.assertEqual(field_values, flat)
+    restructured_from_flat = nest.pack_sequence_as(sample_attr, flat)
+    self.assertIsInstance(restructured_from_flat, NestTest.SampleAttr)
+    self.assertEqual(restructured_from_flat, sample_attr)
+
+    # Check that flatten fails if attributes are not iterable
+    with self.assertRaisesRegexp(TypeError, "object is not iterable"):
+      flat = nest.flatten(NestTest.BadAttr())
+
+  @test_util.assert_no_new_pyobjects_executing_eagerly
+  def testFlattenAndPack(self):
+    structure = ((3, 4), 5, (6, 7, (9, 10), 8))
+    flat = ["a", "b", "c", "d", "e", "f", "g", "h"]
+    self.assertEqual(nest.flatten(structure), [3, 4, 5, 6, 7, 9, 10, 8])
+    self.assertEqual(
+        nest.pack_sequence_as(structure, flat), (("a", "b"), "c",
+                                                 ("d", "e", ("f", "g"), "h")))
+    structure = (NestTest.PointXY(x=4, y=2),
+                 ((NestTest.PointXY(x=1, y=0),),))
+    flat = [4, 2, 1, 0]
+    self.assertEqual(nest.flatten(structure), flat)
+    restructured_from_flat = nest.pack_sequence_as(structure, flat)
+    self.assertEqual(restructured_from_flat, structure)
+    self.assertEqual(restructured_from_flat[0].x, 4)
+    self.assertEqual(restructured_from_flat[0].y, 2)
+    self.assertEqual(restructured_from_flat[1][0][0].x, 1)
+    self.assertEqual(restructured_from_flat[1][0][0].y, 0)
+
+    self.assertEqual([5], nest.flatten(5))
+    self.assertEqual([np.array([5])], nest.flatten(np.array([5])))
+
+    self.assertEqual("a", nest.pack_sequence_as(5, ["a"]))
+    self.assertEqual(
+        np.array([5]), nest.pack_sequence_as("scalar", [np.array([5])]))
+
+    with self.assertRaisesRegexp(ValueError, "Structure is a scalar"):
+      nest.pack_sequence_as("scalar", [4, 5])
+
+    with self.assertRaisesRegexp(TypeError, "flat_sequence"):
+      nest.pack_sequence_as([4, 5], "bad_sequence")
+
+    with self.assertRaises(ValueError):
+      nest.pack_sequence_as([5, 6, [7, 8]], ["a", "b", "c"])
+
+  @parameterized.parameters({"mapping_type": collections.OrderedDict},
+                            {"mapping_type": _CustomMapping})
+  @test_util.assert_no_new_pyobjects_executing_eagerly
+  def testFlattenDictOrder(self, mapping_type):
+    """`flatten` orders dicts by key, including OrderedDicts."""
+    ordered = mapping_type([("d", 3), ("b", 1), ("a", 0), ("c", 2)])
+    plain = {"d": 3, "b": 1, "a": 0, "c": 2}
+    ordered_flat = nest.flatten(ordered)
+    plain_flat = nest.flatten(plain)
+    self.assertEqual([0, 1, 2, 3], ordered_flat)
+    self.assertEqual([0, 1, 2, 3], plain_flat)
+
+  @parameterized.parameters({"mapping_type": collections.OrderedDict},
+                            {"mapping_type": _CustomMapping})
+  def testPackDictOrder(self, mapping_type):
+    """Packing orders dicts by key, including OrderedDicts."""
+    custom = mapping_type([("d", 0), ("b", 0), ("a", 0), ("c", 0)])
+    plain = {"d": 0, "b": 0, "a": 0, "c": 0}
+    seq = [0, 1, 2, 3]
+    custom_reconstruction = nest.pack_sequence_as(custom, seq)
+    plain_reconstruction = nest.pack_sequence_as(plain, seq)
+    self.assertIsInstance(custom_reconstruction, mapping_type)
+    self.assertIsInstance(plain_reconstruction, dict)
+    self.assertEqual(
+        mapping_type([("d", 3), ("b", 1), ("a", 0), ("c", 2)]),
+        custom_reconstruction)
+    self.assertEqual({"d": 3, "b": 1, "a": 0, "c": 2}, plain_reconstruction)
+
+  Abc = collections.namedtuple("A", ("b", "c"))  # pylint: disable=invalid-name
+
+  @test_util.assert_no_new_pyobjects_executing_eagerly
+  def testFlattenAndPack_withDicts(self):
+    # A nice messy mix of tuples, lists, dicts, and `OrderedDict`s.
+    mess = [
+        "z",
+        NestTest.Abc(3, 4), {
+            "d": _CustomMapping({
+                41: 4
+            }),
+            "c": [
+                1,
+                collections.OrderedDict([
+                    ("b", 3),
+                    ("a", 2),
+                ]),
+            ],
+            "b": 5
+        }, 17
+    ]
+
+    flattened = nest.flatten(mess)
+    self.assertEqual(flattened, ["z", 3, 4, 5, 1, 2, 3, 4, 17])
+
+    structure_of_mess = [
+        14,
+        NestTest.Abc("a", True),
+        {
+            "d": _CustomMapping({
+                41: 42
+            }),
+            "c": [
+                0,
+                collections.OrderedDict([
+                    ("b", 9),
+                    ("a", 8),
+                ]),
+            ],
+            "b": 3
+        },
+        "hi everybody",
+    ]
+
+    unflattened = nest.pack_sequence_as(structure_of_mess, flattened)
+    self.assertEqual(unflattened, mess)
+
+    # Check also that the OrderedDict was created, with the correct key order.
+    unflattened_ordered_dict = unflattened[2]["c"][1]
+    self.assertIsInstance(unflattened_ordered_dict, collections.OrderedDict)
+    self.assertEqual(list(unflattened_ordered_dict.keys()), ["b", "a"])
+
+    unflattened_custom_mapping = unflattened[2]["d"]
+    self.assertIsInstance(unflattened_custom_mapping, _CustomMapping)
+    self.assertEqual(list(unflattened_custom_mapping.keys()), [41])
+
+  def testFlatten_numpyIsNotFlattened(self):
+    structure = np.array([1, 2, 3])
+    flattened = nest.flatten(structure)
+    self.assertEqual(len(flattened), 1)
+
+  def testFlatten_stringIsNotFlattened(self):
+    structure = "lots of letters"
+    flattened = nest.flatten(structure)
+    self.assertEqual(len(flattened), 1)
+    unflattened = nest.pack_sequence_as("goodbye", flattened)
+    self.assertEqual(structure, unflattened)
+
+  def testPackSequenceAs_notIterableError(self):
+    with self.assertRaisesRegexp(TypeError,
+                                 "flat_sequence must be a sequence"):
+      nest.pack_sequence_as("hi", "bye")
+
+  def testPackSequenceAs_wrongLengthsError(self):
+    with self.assertRaisesRegexp(
+        ValueError,
+        "Structure had 2 elements, but flat_sequence had 3 elements."):
+      nest.pack_sequence_as(["hello", "world"],
+                            ["and", "goodbye", "again"])
+
+  @test_util.assert_no_new_pyobjects_executing_eagerly
+  def testIsSequence(self):
+    self.assertFalse(nest.is_sequence("1234"))
+    self.assertTrue(nest.is_sequence([1, 3, [4, 5]]))
+    self.assertTrue(nest.is_sequence(((7, 8), (5, 6))))
+    self.assertTrue(nest.is_sequence([]))
+    self.assertTrue(nest.is_sequence({"a": 1, "b": 2}))
+    self.assertFalse(nest.is_sequence(set([1, 2])))
+    ones = array_ops.ones([2, 3])
+    self.assertFalse(nest.is_sequence(ones))
+    self.assertFalse(nest.is_sequence(math_ops.tanh(ones)))
+    self.assertFalse(nest.is_sequence(np.ones((4, 5))))
+
+  @parameterized.parameters({"mapping_type": _CustomMapping},
+                            {"mapping_type": dict})
+  def testFlattenDictItems(self, mapping_type):
+    dictionary = mapping_type({(4, 5, (6, 8)): ("a", "b", ("c", "d"))})
+    flat = {4: "a", 5: "b", 6: "c", 8: "d"}
+    self.assertEqual(nest.flatten_dict_items(dictionary), flat)
+
+    with self.assertRaises(TypeError):
+      nest.flatten_dict_items(4)
+
+    bad_dictionary = mapping_type({(4, 5, (4, 8)): ("a", "b", ("c", "d"))})
+    with self.assertRaisesRegexp(ValueError, "not unique"):
+      nest.flatten_dict_items(bad_dictionary)
+
+    another_bad_dictionary = mapping_type({
+        (4, 5, (6, 8)): ("a", "b", ("c", ("d", "e")))
+    })
+    with self.assertRaisesRegexp(
+        ValueError, "Key had [0-9]* elements, but value had [0-9]* elements"):
+      nest.flatten_dict_items(another_bad_dictionary)
+
+  # pylint does not correctly recognize these as class names and
+  # suggests to use variable style under_score naming.
+  # pylint: disable=invalid-name
+  Named0ab = collections.namedtuple("named_0", ("a", "b"))
+  Named1ab = collections.namedtuple("named_1", ("a", "b"))
+  SameNameab = collections.namedtuple("same_name", ("a", "b"))
+  SameNameab2 = collections.namedtuple("same_name", ("a", "b"))
+  SameNamexy = collections.namedtuple("same_name", ("x", "y"))
+  SameName1xy = collections.namedtuple("same_name_1", ("x", "y"))
+  SameName1xy2 = collections.namedtuple("same_name_1", ("x", "y"))
+  NotSameName = collections.namedtuple("not_same_name", ("a", "b"))
+  # pylint: enable=invalid-name
+
+  class SameNamedType1(SameNameab):
+    pass
+
+  @test_util.assert_no_new_pyobjects_executing_eagerly
+  def testAssertSameStructure(self):
+    structure1 = (((1, 2), 3), 4, (5, 6))
+    structure2 = ((("foo1", "foo2"), "foo3"), "foo4", ("foo5", "foo6"))
+    structure_different_num_elements = ("spam", "eggs")
+    structure_different_nesting = (((1, 2), 3), 4, 5, (6,))
+    nest.assert_same_structure(structure1, structure2)
+    nest.assert_same_structure("abc", 1.0)
+    nest.assert_same_structure("abc", np.array([0, 1]))
+    nest.assert_same_structure("abc", constant_op.constant([0, 1]))
+
+    with self.assertRaisesRegexp(
+        ValueError,
+        ("The two structures don't have the same nested structure\\.\n\n"
+         "First structure:.*?\n\n"
+         "Second structure:.*\n\n"
+         "More specifically: Substructure "
+         r'"type=tuple str=\(\(1, 2\), 3\)" is a sequence, while '
+         'substructure "type=str str=spam" is not\n'
+         "Entire first structure:\n"
+         r"\(\(\(\., \.\), \.\), \., \(\., \.\)\)\n"
+         "Entire second structure:\n"
+         r"\(\., \.\)")):
+      nest.assert_same_structure(structure1, structure_different_num_elements)
+
+    with self.assertRaisesRegexp(
+        ValueError,
+        ("The two structures don't have the same nested structure\\.\n\n"
+         "First structure:.*?\n\n"
+         "Second structure:.*\n\n"
+         r'More specifically: Substructure "type=list str=\[0, 1\]" '
+         r'is a sequence, while substructure "type=ndarray str=\[0 1\]" '
+         "is not")):
+      nest.assert_same_structure([0, 1], np.array([0, 1]))
+
+    with self.assertRaisesRegexp(
+        ValueError,
+        ("The two structures don't have the same nested structure\\.\n\n"
+         "First structure:.*?\n\n"
+         "Second structure:.*\n\n"
+         r'More specifically: Substructure "type=list str=\[0, 1\]" '
+         'is a sequence, while substructure "type=int str=0" '
+         "is not")):
+      nest.assert_same_structure(0, [0, 1])
+
+    self.assertRaises(TypeError, nest.assert_same_structure, (0, 1), [0, 1])
+
+    with self.assertRaisesRegexp(
+        ValueError,
+        ("don't have the same nested structure\\.\n\n"
+         "First structure: .*?\n\nSecond structure: ")):
+      nest.assert_same_structure(structure1, structure_different_nesting)
+
+    self.assertRaises(TypeError, nest.assert_same_structure, (0, 1),
+                      NestTest.Named0ab("a", "b"))
+
+    nest.assert_same_structure(NestTest.Named0ab(3, 4),
+                               NestTest.Named0ab("a", "b"))
+
+    self.assertRaises(TypeError, nest.assert_same_structure,
+                      NestTest.Named0ab(3, 4), NestTest.Named1ab(3, 4))
+
+    with self.assertRaisesRegexp(
+        ValueError,
+        ("don't have the same nested structure\\.\n\n"
+         "First structure: .*?\n\nSecond structure: ")):
+      nest.assert_same_structure(NestTest.Named0ab(3, 4),
+                                 NestTest.Named0ab([3], 4))
+
+    with self.assertRaisesRegexp(
+        ValueError,
+        ("don't have the same nested structure\\.\n\n"
+         "First structure: .*?\n\nSecond structure: ")):
+      nest.assert_same_structure([[3], 4], [3, [4]])
+
+    structure1_list = [[[1, 2], 3], 4, [5, 6]]
+    with self.assertRaisesRegexp(TypeError,
+                                 "don't have the same sequence type"):
+      nest.assert_same_structure(structure1, structure1_list)
+    nest.assert_same_structure(structure1, structure2, check_types=False)
+    nest.assert_same_structure(structure1, structure1_list, check_types=False)
+
+    with self.assertRaisesRegexp(ValueError,
+                                 "don't have the same set of keys"):
+      nest.assert_same_structure({"a": 1}, {"b": 1})
+
+    nest.assert_same_structure(NestTest.SameNameab(0, 1),
+                               NestTest.SameNameab2(2, 3))
+
+    # This assertion is expected to pass: two namedtuples with the same
+    # name and field names are considered to be identical.
+    nest.assert_same_structure(
+        NestTest.SameNameab(NestTest.SameName1xy(0, 1), 2),
+        NestTest.SameNameab2(NestTest.SameName1xy2(2, 3), 4))
+
+    expected_message = "The two structures don't have the same.*"
+    with self.assertRaisesRegexp(ValueError, expected_message):
+      nest.assert_same_structure(
+          NestTest.SameNameab(0, NestTest.SameNameab2(1, 2)),
+          NestTest.SameNameab2(NestTest.SameNameab(0, 1), 2))
+
+    self.assertRaises(TypeError, nest.assert_same_structure,
+                      NestTest.SameNameab(0, 1), NestTest.NotSameName(2, 3))
+
+    self.assertRaises(TypeError, nest.assert_same_structure,
+                      NestTest.SameNameab(0, 1), NestTest.SameNamexy(2, 3))
+
+    self.assertRaises(TypeError, nest.assert_same_structure,
+                      NestTest.SameNameab(0, 1), NestTest.SameNamedType1(2, 3))
+
+  EmptyNT = collections.namedtuple("empty_nt", "")  # pylint: disable=invalid-name
+
+  def testHeterogeneousComparison(self):
+    nest.assert_same_structure({"a": 4}, _CustomMapping(a=3))
+    nest.assert_same_structure(_CustomMapping(b=3), {"b": 4})
+
+  @test_util.assert_no_new_pyobjects_executing_eagerly
+  def testMapStructure(self):
+    structure1 = (((1, 2), 3), 4, (5, 6))
+    structure2 = (((7, 8), 9), 10, (11, 12))
+    structure1_plus1 = nest.map_structure(lambda x: x + 1, structure1)
+    nest.assert_same_structure(structure1, structure1_plus1)
+    self.assertAllEqual(
+        [2, 3, 4, 5, 6, 7],
+        nest.flatten(structure1_plus1))
+    structure1_plus_structure2 = nest.map_structure(
+        lambda x, y: x + y, structure1, structure2)
+    self.assertEqual(
+        (((1 + 7, 2 + 8), 3 + 9), 4 + 10, (5 + 11, 6 + 12)),
+        structure1_plus_structure2)
+
+    self.assertEqual(3, nest.map_structure(lambda x: x - 1, 4))
+
+    self.assertEqual(7, nest.map_structure(lambda x, y: x + y, 3, 4))
+
+    # Empty structures
+    self.assertEqual((), nest.map_structure(lambda x: x + 1, ()))
+    self.assertEqual([], nest.map_structure(lambda x: x + 1, []))
+    self.assertEqual({}, nest.map_structure(lambda x: x + 1, {}))
+    self.assertEqual(NestTest.EmptyNT(), nest.map_structure(lambda x: x + 1,
+                                                            NestTest.EmptyNT()))
+
+    # This is checking actual equality of types, empty list != empty tuple
+    self.assertNotEqual((), nest.map_structure(lambda x: x + 1, []))
+
+    with self.assertRaisesRegexp(TypeError, "callable"):
+      nest.map_structure("bad", structure1_plus1)
+
+    with self.assertRaisesRegexp(ValueError, "at least one structure"):
+      nest.map_structure(lambda x: x)
+
+    with self.assertRaisesRegexp(ValueError, "same number of elements"):
+      nest.map_structure(lambda x, y: None, (3, 4), (3, 4, 5))
+
+    with self.assertRaisesRegexp(ValueError, "same nested structure"):
+      nest.map_structure(lambda x, y: None, 3, (3,))
+
+    with self.assertRaisesRegexp(TypeError, "same sequence type"):
+      nest.map_structure(lambda x, y: None, ((3, 4), 5), [(3, 4), 5])
+
+    with self.assertRaisesRegexp(ValueError, "same nested structure"):
+      nest.map_structure(lambda x, y: None, ((3, 4), 5), (3, (4, 5)))
+
+    structure1_list = [[[1, 2], 3], 4, [5, 6]]
+    with self.assertRaisesRegexp(TypeError, "same sequence type"):
+      nest.map_structure(lambda x, y: None, structure1, structure1_list)
+
+    nest.map_structure(lambda x, y: None, structure1, structure1_list,
+                       check_types=False)
+
+    with self.assertRaisesRegexp(ValueError, "same nested structure"):
+      nest.map_structure(lambda x, y: None, ((3, 4), 5), (3, (4, 5)),
+                         check_types=False)
+
+    with self.assertRaisesRegexp(ValueError, "Only valid keyword argument"):
+      nest.map_structure(lambda x: None, structure1, foo="a")
+
+    with self.assertRaisesRegexp(ValueError, "Only valid keyword argument"):
+      nest.map_structure(lambda x: None, structure1, check_types=False, foo="a")
+
+  ABTuple = collections.namedtuple("ab_tuple", "a, b")  # pylint: disable=invalid-name
+
+  @test_util.assert_no_new_pyobjects_executing_eagerly
+  def testMapStructureWithStrings(self):
+    inp_a = NestTest.ABTuple(a="foo", b=("bar", "baz"))
+    inp_b = NestTest.ABTuple(a=2, b=(1, 3))
+    out = nest.map_structure(lambda string, repeats: string * repeats,
+                             inp_a,
+                             inp_b)
+    self.assertEqual("foofoo", out.a)
+    self.assertEqual("bar", out.b[0])
+    self.assertEqual("bazbazbaz", out.b[1])
+
+    nt = NestTest.ABTuple(a=("something", "something_else"),
+                          b="yet another thing")
+    rev_nt = nest.map_structure(lambda x: x[::-1], nt)
+    # Check the output is the correct structure, and all strings are reversed.
+    nest.assert_same_structure(nt, rev_nt)
+    self.assertEqual(nt.a[0][::-1], rev_nt.a[0])
+    self.assertEqual(nt.a[1][::-1], rev_nt.a[1])
+    self.assertEqual(nt.b[::-1], rev_nt.b)
+
+  @test_util.run_deprecated_v1
+  def testMapStructureOverPlaceholders(self):
+    inp_a = (array_ops.placeholder(dtypes.float32, shape=[3, 4]),
+             array_ops.placeholder(dtypes.float32, shape=[3, 7]))
+    inp_b = (array_ops.placeholder(dtypes.float32, shape=[3, 4]),
+             array_ops.placeholder(dtypes.float32, shape=[3, 7]))
+
+    output = nest.map_structure(lambda x1, x2: x1 + x2, inp_a, inp_b)
+
+    nest.assert_same_structure(output, inp_a)
+    self.assertShapeEqual(np.zeros((3, 4)), output[0])
+    self.assertShapeEqual(np.zeros((3, 7)), output[1])
+
+    feed_dict = {
+        inp_a: (np.random.randn(3, 4), np.random.randn(3, 7)),
+        inp_b: (np.random.randn(3, 4), np.random.randn(3, 7))
+    }
+
+    with self.cached_session() as sess:
+      output_np = sess.run(output, feed_dict=feed_dict)
+    self.assertAllClose(output_np[0],
+                        feed_dict[inp_a][0] + feed_dict[inp_b][0])
+    self.assertAllClose(output_np[1],
+                        feed_dict[inp_a][1] + feed_dict[inp_b][1])
+
+  def testAssertShallowStructure(self):
+    inp_ab = ["a", "b"]
+    inp_abc = ["a", "b", "c"]
+    expected_message = (
+        "The two structures don't have the same sequence length. Input "
+        "structure has length 2, while shallow structure has length 3.")
+    with self.assertRaisesRegexp(ValueError, expected_message):
+      nest.assert_shallow_structure(inp_abc, inp_ab)
+
+    inp_ab1 = [(1, 1), (2, 2)]
+    inp_ab2 = [[1, 1], [2, 2]]
+    expected_message = (
+        "The two structures don't have the same sequence type. Input structure "
+        "has type <(type|class) 'tuple'>, while shallow structure has type "
+        "<(type|class) 'list'>.")
+    with self.assertRaisesRegexp(TypeError, expected_message):
+      nest.assert_shallow_structure(inp_ab2, inp_ab1)
+    nest.assert_shallow_structure(inp_ab2, inp_ab1, check_types=False)
+
+    inp_ab1 = {"a": (1, 1), "b": {"c": (2, 2)}}
+    inp_ab2 = {"a": (1, 1), "b": {"d": (2, 2)}}
+    expected_message = (
+        r"The two structures don't have the same keys. Input "
+        r"structure has keys \['c'\], while shallow structure has "
+        r"keys \['d'\].")
+
+    with self.assertRaisesRegexp(ValueError, expected_message):
+      nest.assert_shallow_structure(inp_ab2, inp_ab1)
+
+    inp_ab = collections.OrderedDict([("a", 1), ("b", (2, 3))])
+    inp_ba = collections.OrderedDict([("b", (2, 3)), ("a", 1)])
+    nest.assert_shallow_structure(inp_ab, inp_ba)
+
+    # This assertion is expected to pass: two namedtuples with the same
+    # name and field names are considered to be identical.
+    inp_shallow = NestTest.SameNameab(1, 2)
+    inp_deep = NestTest.SameNameab2(1, [1, 2, 3])
+    nest.assert_shallow_structure(inp_shallow, inp_deep, check_types=False)
+    nest.assert_shallow_structure(inp_shallow, inp_deep, check_types=True)
+
+  def testFlattenUpTo(self):
+    # Shallow tree ends at scalar.
+    input_tree = [[[2, 2], [3, 3]], [[4, 9], [5, 5]]]
+    shallow_tree = [[True, True], [False, True]]
+    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_input_tree, [[2, 2], [3, 3], [4, 9], [5, 5]])
+    self.assertEqual(flattened_shallow_tree, [True, True, False, True])
+
+    # Shallow tree ends at string.
+    input_tree = [[("a", 1), [("b", 2), [("c", 3), [("d", 4)]]]]]
+    shallow_tree = [["level_1", ["level_2", ["level_3", ["level_4"]]]]]
+    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+                                                              input_tree)
+    input_tree_flattened = nest.flatten(input_tree)
+    self.assertEqual(input_tree_flattened_as_shallow_tree,
+                     [("a", 1), ("b", 2), ("c", 3), ("d", 4)])
+    self.assertEqual(input_tree_flattened, ["a", 1, "b", 2, "c", 3, "d", 4])
+
+    # Make sure dicts are correctly flattened, yielding values, not keys.
+    input_tree = {"a": 1, "b": {"c": 2}, "d": [3, (4, 5)]}
+    shallow_tree = {"a": 0, "b": 0, "d": [0, 0]}
+    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+                                                              input_tree)
+    self.assertEqual(input_tree_flattened_as_shallow_tree,
+                     [1, {"c": 2}, 3, (4, 5)])
+
+    # Namedtuples.
+    ab_tuple = NestTest.ABTuple
+    input_tree = ab_tuple(a=[0, 1], b=2)
+    shallow_tree = ab_tuple(a=0, b=1)
+    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+                                                              input_tree)
+    self.assertEqual(input_tree_flattened_as_shallow_tree,
+                     [[0, 1], 2])
+
+    # Nested dicts, OrderedDicts and namedtuples.
+    input_tree = collections.OrderedDict(
+        [("a", ab_tuple(a=[0, {"b": 1}], b=2)),
+         ("c", {"d": 3, "e": collections.OrderedDict([("f", 4)])})])
+    shallow_tree = input_tree
+    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+                                                              input_tree)
+    self.assertEqual(input_tree_flattened_as_shallow_tree, [0, 1, 2, 3, 4])
+    shallow_tree = collections.OrderedDict([("a", 0), ("c", {"d": 3, "e": 1})])
+    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+                                                              input_tree)
+    self.assertEqual(input_tree_flattened_as_shallow_tree,
+                     [ab_tuple(a=[0, {"b": 1}], b=2),
+                      3,
+                      collections.OrderedDict([("f", 4)])])
+    shallow_tree = collections.OrderedDict([("a", 0), ("c", 0)])
+    input_tree_flattened_as_shallow_tree = nest.flatten_up_to(shallow_tree,
+                                                              input_tree)
+    self.assertEqual(input_tree_flattened_as_shallow_tree,
+                     [ab_tuple(a=[0, {"b": 1}], b=2),
+                      {"d": 3, "e": collections.OrderedDict([("f", 4)])}])
+
+    ## Shallow non-list edge-case.
+    # Using iterable elements.
+    input_tree = ["input_tree"]
+    shallow_tree = "shallow_tree"
+    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_input_tree, [input_tree])
+    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+    input_tree = ["input_tree_0", "input_tree_1"]
+    shallow_tree = "shallow_tree"
+    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_input_tree, [input_tree])
+    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+    # Using non-iterable elements.
+    input_tree = [0]
+    shallow_tree = 9
+    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_input_tree, [input_tree])
+    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+    input_tree = [0, 1]
+    shallow_tree = 9
+    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_input_tree, [input_tree])
+    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+    ## Both non-list edge-case.
+    # Using iterable elements.
+    input_tree = "input_tree"
+    shallow_tree = "shallow_tree"
+    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_input_tree, [input_tree])
+    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+    # Using non-iterable elements.
+    input_tree = 0
+    shallow_tree = 0
+    flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_input_tree, [input_tree])
+    self.assertEqual(flattened_shallow_tree, [shallow_tree])
+
+    ## Input non-list edge-case.
+    # Using iterable elements.
+    input_tree = "input_tree"
+    shallow_tree = ["shallow_tree"]
+    expected_message = ("If shallow structure is a sequence, input must also "
+                        "be a sequence. Input has type: <(type|class) 'str'>.")
+    with self.assertRaisesRegexp(TypeError, expected_message):
+      flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_shallow_tree, shallow_tree)
+
+    input_tree = "input_tree"
+    shallow_tree = ["shallow_tree_9", "shallow_tree_8"]
+    with self.assertRaisesRegexp(TypeError, expected_message):
+      flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_shallow_tree, shallow_tree)
+
+    # Using non-iterable elements.
+    input_tree = 0
+    shallow_tree = [9]
+    expected_message = ("If shallow structure is a sequence, input must also "
+                        "be a sequence. Input has type: <(type|class) 'int'>.")
+    with self.assertRaisesRegexp(TypeError, expected_message):
+      flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_shallow_tree, shallow_tree)
+
+    input_tree = 0
+    shallow_tree = [9, 8]
+    with self.assertRaisesRegexp(TypeError, expected_message):
+      flattened_input_tree = nest.flatten_up_to(shallow_tree, input_tree)
+    flattened_shallow_tree = nest.flatten_up_to(shallow_tree, shallow_tree)
+    self.assertEqual(flattened_shallow_tree, shallow_tree)
+
+  def testMapStructureUpTo(self):
+    # Named tuples.
+    ab_tuple = collections.namedtuple("ab_tuple", "a, b")
+    op_tuple = collections.namedtuple("op_tuple", "add, mul")
+    inp_val = ab_tuple(a=2, b=3)
+    inp_ops = ab_tuple(a=op_tuple(add=1, mul=2), b=op_tuple(add=2, mul=3))
+    out = nest.map_structure_up_to(
+        inp_val, lambda val, ops: (val + ops.add) * ops.mul, inp_val, inp_ops)
+    self.assertEqual(out.a, 6)
+    self.assertEqual(out.b, 15)
+
+    # Lists.
+    data_list = [[2, 4, 6, 8], [[1, 3, 5, 7, 9], [3, 5, 7]]]
+    name_list = ["evens", ["odds", "primes"]]
+    out = nest.map_structure_up_to(
+        name_list, lambda name, sec: "first_{}_{}".format(len(sec), name),
+        name_list, data_list)
+    self.assertEqual(out, ["first_4_evens", ["first_5_odds", "first_3_primes"]])
+
+    # Dicts.
+    inp_val = dict(a=2, b=3)
+    inp_ops = dict(a=dict(add=1, mul=2), b=dict(add=2, mul=3))
+    out = nest.map_structure_up_to(
+        inp_val,
+        lambda val, ops: (val + ops["add"]) * ops["mul"], inp_val, inp_ops)
+    self.assertEqual(out["a"], 6)
+    self.assertEqual(out["b"], 15)
+
+    # Non-equal dicts.
+    inp_val = dict(a=2, b=3)
+    inp_ops = dict(a=dict(add=1, mul=2), c=dict(add=2, mul=3))
+    with self.assertRaisesRegexp(ValueError, "same keys"):
+      nest.map_structure_up_to(
+          inp_val,
+          lambda val, ops: (val + ops["add"]) * ops["mul"], inp_val, inp_ops)
+
+    # Dict+custom mapping.
+    inp_val = dict(a=2, b=3)
+    inp_ops = _CustomMapping(a=dict(add=1, mul=2), b=dict(add=2, mul=3))
+    out = nest.map_structure_up_to(
+        inp_val,
+        lambda val, ops: (val + ops["add"]) * ops["mul"], inp_val, inp_ops)
+    self.assertEqual(out["a"], 6)
+    self.assertEqual(out["b"], 15)
+
+    # Non-equal dict/mapping.
+    inp_val = dict(a=2, b=3)
+    inp_ops = _CustomMapping(a=dict(add=1, mul=2), c=dict(add=2, mul=3))
+    with self.assertRaisesRegexp(ValueError, "same keys"):
+      nest.map_structure_up_to(
+          inp_val,
+          lambda val, ops: (val + ops["add"]) * ops["mul"], inp_val, inp_ops)
+
+  def testGetTraverseShallowStructure(self):
+    scalar_traverse_input = [3, 4, (1, 2, [0]), [5, 6], {"a": (7,)}, []]
+    scalar_traverse_r = nest.get_traverse_shallow_structure(
+        lambda s: not isinstance(s, tuple),
+        scalar_traverse_input)
+    self.assertEqual(scalar_traverse_r,
+                     [True, True, False, [True, True], {"a": False}, []])
+    nest.assert_shallow_structure(scalar_traverse_r,
+                                  scalar_traverse_input)
+
+    structure_traverse_input = [(1, [2]), ([1], 2)]
+    structure_traverse_r = nest.get_traverse_shallow_structure(
+        lambda s: (True, False) if isinstance(s, tuple) else True,
+        structure_traverse_input)
+    self.assertEqual(structure_traverse_r,
+                     [(True, False), ([True], False)])
+    nest.assert_shallow_structure(structure_traverse_r,
+                                  structure_traverse_input)
+
+    with self.assertRaisesRegexp(TypeError, "returned structure"):
+      nest.get_traverse_shallow_structure(lambda _: [True], 0)
+
+    with self.assertRaisesRegexp(TypeError, "returned a non-bool scalar"):
+      nest.get_traverse_shallow_structure(lambda _: 1, [1])
+
+    with self.assertRaisesRegexp(
+        TypeError, "didn't return a depth=1 structure of bools"):
+      nest.get_traverse_shallow_structure(lambda _: [1], [1])
+
+  def testYieldFlatStringPaths(self):
+    for inputs_expected in ({"inputs": [], "expected": []},
+                            {"inputs": 3, "expected": [()]},
+                            {"inputs": [3], "expected": [(0,)]},
+                            {"inputs": {"a": 3}, "expected": [("a",)]},
+                            {"inputs": {"a": {"b": 4}},
+                             "expected": [("a", "b")]},
+                            {"inputs": [{"a": 2}], "expected": [(0, "a")]},
+                            {"inputs": [{"a": [2]}], "expected": [(0, "a", 0)]},
+                            {"inputs": [{"a": [(23, 42)]}],
+                             "expected": [(0, "a", 0, 0), (0, "a", 0, 1)]},
+                            {"inputs": [{"a": ([23], 42)}],
+                             "expected": [(0, "a", 0, 0), (0, "a", 1)]},
+                            {"inputs": {"a": {"a": 2}, "c": [[[4]]]},
+                             "expected": [("a", "a"), ("c", 0, 0, 0)]},
+                            {"inputs": {"0": [{"1": 23}]},
+                             "expected": [("0", 0, "1")]}):
+      inputs = inputs_expected["inputs"]
+      expected = inputs_expected["expected"]
+      self.assertEqual(list(nest.yield_flat_paths(inputs)), expected)
+
+  def testFlattenWithStringPaths(self):
+    for inputs_expected in (
+        {"inputs": [], "expected": []},
+        {"inputs": [23, "42"], "expected": [("0", 23), ("1", "42")]},
+        {"inputs": [[[[108]]]], "expected": [("0/0/0/0", 108)]}):
+      inputs = inputs_expected["inputs"]
+      expected = inputs_expected["expected"]
+      self.assertEqual(
+          nest.flatten_with_joined_string_paths(inputs, separator="/"),
+          expected)
+
+  # Need a separate test for namedtuple as we can't declare tuple definitions
+  # in the @parameterized arguments.
+  def testFlattenNamedTuple(self):
+    # pylint: disable=invalid-name
+    Foo = collections.namedtuple("Foo", ["a", "b"])
+    Bar = collections.namedtuple("Bar", ["c", "d"])
+    # pylint: enable=invalid-name
+    test_cases = [
+        (Foo(a=3, b=Bar(c=23, d=42)),
+         [("a", 3), ("b/c", 23), ("b/d", 42)]),
+        (Foo(a=Bar(c=23, d=42), b=Bar(c=0, d="something")),
+         [("a/c", 23), ("a/d", 42), ("b/c", 0), ("b/d", "something")]),
+        (Bar(c=42, d=43),
+         [("c", 42), ("d", 43)]),
+        (Bar(c=[42], d=43),
+         [("c/0", 42), ("d", 43)]),
+    ]
+    for inputs, expected in test_cases:
+      self.assertEqual(
+          list(nest.flatten_with_joined_string_paths(inputs)), expected)
+
+  @parameterized.named_parameters(
+      ("tuples", (1, 2), (3, 4), True, (("0", 4), ("1", 6))),
+      ("dicts", {"a": 1, "b": 2}, {"b": 4, "a": 3}, True,
+       {"a": ("a", 4), "b": ("b", 6)}),
+      ("mixed", (1, 2), [3, 4], False, (("0", 4), ("1", 6))),
+      ("nested",
+       {"a": [2, 3], "b": [1, 2, 3]}, {"b": [5, 6, 7], "a": [8, 9]}, True,
+       {"a": [("a/0", 10), ("a/1", 12)],
+        "b": [("b/0", 6), ("b/1", 8), ("b/2", 10)]}))
+  def testMapWithPathsCompatibleStructures(self, s1, s2, check_types, expected):
+    def format_sum(path, *values):
+      return (path, sum(values))
+    result = nest.map_structure_with_paths(format_sum, s1, s2,
+                                           check_types=check_types)
+    self.assertEqual(expected, result)
+
+  @parameterized.named_parameters(
+      ("tuples", (1, 2), (3, 4, 5), ValueError),
+      ("dicts", {"a": 1}, {"b": 2}, ValueError),
+      ("mixed", (1, 2), [3, 4], TypeError),
+      ("nested",
+       {"a": [2, 3], "b": [1, 3]},
+       {"b": [5, 6, 7], "a": [8, 9]},
+       ValueError
+      ))
+  def testMapWithPathsIncompatibleStructures(self, s1, s2, error_type):
+    with self.assertRaises(error_type):
+      nest.map_structure_with_paths(lambda path, *s: 0, s1, s2)
+
+
+class NestBenchmark(test.Benchmark):
+
+  def run_and_report(self, s1, s2, name):
+    burn_iter, test_iter = 100, 30000
+
+    for _ in xrange(burn_iter):
+      nest.assert_same_structure(s1, s2)
+
+    t0 = time.time()
+    for _ in xrange(test_iter):
+      nest.assert_same_structure(s1, s2)
+    t1 = time.time()
+
+    self.report_benchmark(iters=test_iter, wall_time=(t1 - t0) / test_iter,
+                          name=name)
+
+  def benchmark_assert_structure(self):
+    s1 = (((1, 2), 3), 4, (5, 6))
+    s2 = ((("foo1", "foo2"), "foo3"), "foo4", ("foo5", "foo6"))
+    self.run_and_report(s1, s2, "assert_same_structure_6_elem")
+
+    s1 = (((1, 2), 3), 4, (5, 6)) * 10
+    s2 = ((("foo1", "foo2"), "foo3"), "foo4", ("foo5", "foo6")) * 10
+    self.run_and_report(s1, s2, "assert_same_structure_60_elem")
+
+
+if __name__ == "__main__":
+  test.main()