diff --git a/fastNLP/action/inference.py b/fastNLP/action/inference.py
index 94e5be19..1a1c4d2c 100644
--- a/fastNLP/action/inference.py
+++ b/fastNLP/action/inference.py
@@ -3,9 +3,6 @@ class Inference(object):
     This is an interface focusing on predicting output based on trained models.
     It does not care about evaluations of the model.
 
-    Possible improvements:
-        - use batch to make use of GPU
-
     """
 
     def __init__(self):
diff --git a/fastNLP/action/metrics.py b/fastNLP/action/metrics.py
new file mode 100644
index 00000000..7c8a6bec
--- /dev/null
+++ b/fastNLP/action/metrics.py
@@ -0,0 +1,8 @@
+"""
+To do:
+ 设计评判结果的各种指标。如果涉及向量，使用numpy。
+ 参考http://scikit-learn.org/stable/modules/classes.html#classification-metrics
+ 建议是每种metric写成一个函数 （由Tester的evaluate函数调用）
+ 参数表里只需考虑基本的参数即可，可以没有像它那么多的参数配置
+  
+"""
diff --git a/fastNLP/action/optimizor.py b/fastNLP/action/optimizor.py
index 89a6c7eb..becdc499 100644
--- a/fastNLP/action/optimizor.py
+++ b/fastNLP/action/optimizor.py
@@ -1,15 +1,16 @@
 from torch import optim
 
-def get_torch_optimizor(params, alg_name='sgd', **args):
-    '''
-    construct pytorch optimizor by algorithm's name
-    optimizor's argurments can be splicified, for different optimizor's argurments, please see pytorch doc
+
+def get_torch_optimizer(params, alg_name='sgd', **args):
+    """
+    construct PyTorch optimizer by algorithm's name
+    optimizer's arguments can be specified, for different optimizer's arguments, please see PyTorch doc
 
     usage:
-        optimizor = get_torch_optimizor(model.parameters(), 'SGD', lr=0.01)
+        optimizer = get_torch_optimizer(model.parameters(), 'SGD', lr=0.01)
+
+    """
 
-    '''
-    
     name = alg_name.lower()
     if name == 'adadelta':
         return optim.Adadelta(params, **args)
@@ -28,22 +29,22 @@ def get_torch_optimizor(params, alg_name='sgd', **args):
     elif name == 'rprop':
         return optim.Rprop(params, **args)
     elif name == 'sgd':
-        #SGD's parameter lr is required
+        # SGD's parameter lr is required
         if 'lr' not in args:
             args['lr'] = 0.01
         return optim.SGD(params, **args)
     elif name == 'sparseadam':
         return optim.SparseAdam(params, **args)
     else:
-        raise TypeError('no such optimizor named {}'.format(alg_name))
+        raise TypeError('no such optimizer named {}'.format(alg_name))
 
 
-# example usage
 if __name__ == '__main__':
     from torch.nn.modules import Linear
+
     net = Linear(2, 5)
 
-    test1 = get_torch_optimizor(net.parameters(),'adam', lr=1e-2, weight_decay=1e-3)
+    test1 = get_torch_optimizer(net.parameters(), 'adam', lr=1e-2, weight_decay=1e-3)
     print(test1)
-    test2 = get_torch_optimizor(net.parameters(), 'SGD')
-    print(test2)
\ No newline at end of file
+    test2 = get_torch_optimizer(net.parameters(), 'SGD')
+    print(test2)
diff --git a/fastNLP/action/tester.py b/fastNLP/action/tester.py
index e4cca9e5..6ba8c9fa 100644
--- a/fastNLP/action/tester.py
+++ b/fastNLP/action/tester.py
@@ -1,8 +1,8 @@
 import _pickle
+import os
 
 import numpy as np
 import torch
-import os
 
 from fastNLP.action.action import Action
 from fastNLP.action.action import RandomSampler, Batchifier
@@ -108,7 +108,7 @@ class BaseTester(Action):
         raise NotImplementedError
 
     @property
-    def matrices(self):
+    def metrics(self):
         raise NotImplementedError
 
     def mode(self, model, test=True):
@@ -163,7 +163,7 @@ class POSTester(BaseTester):
         accuracy = float(torch.sum(results == truth.view((-1,)))) / results.shape[0]
         return [loss.data, accuracy]
 
-    def matrices(self):
+    def metrics(self):
         batch_loss = np.mean([x[0] for x in self.eval_history])
         batch_accuracy = np.mean([x[1] for x in self.eval_history])
         return batch_loss, batch_accuracy
@@ -173,7 +173,7 @@ class POSTester(BaseTester):
         This is called by Trainer to print evaluation on dev set.
         :return print_str: str
         """
-        loss, accuracy = self.matrices()
+        loss, accuracy = self.metrics()
         return "dev loss={:.2f}, accuracy={:.2f}".format(loss, accuracy)
 
 
@@ -309,7 +309,7 @@ class ClassTester(BaseTester):
         y_prob = torch.nn.functional.softmax(y_logit, dim=-1)
         return [y_prob, y_true]
 
-    def matrices(self):
+    def metrics(self):
         """Compute accuracy."""
         y_prob, y_true = zip(*self.eval_history)
         y_prob = torch.cat(y_prob, dim=0)
diff --git a/fastNLP/action/trainer.py b/fastNLP/action/trainer.py
index 45049e9d..419fceca 100644
--- a/fastNLP/action/trainer.py
+++ b/fastNLP/action/trainer.py
@@ -181,7 +181,7 @@ class BaseTrainer(Action):
         """
         raise NotImplementedError
 
-    def batchify(self, data):
+    def batchify(self, data, output_length=True):
         """
         1. Perform batching from data and produce a batch of training data.
         2. Add padding.
@@ -194,13 +194,18 @@ class BaseTrainer(Action):
                 ]
         :return batch_x: list. Each entry is a list of features of a sample. [batch_size, max_len]
                  batch_y: list. Each entry is a list of labels of a sample.  [batch_size, num_labels]
+                 seq_len: list. The length of the pre-padded sequence, if output_length is True.
         """
         indices = next(self.iterator)
         batch = [data[idx] for idx in indices]
         batch_x = [sample[0] for sample in batch]
         batch_y = [sample[1] for sample in batch]
-        batch_x = self.pad(batch_x)
-        return batch_x, batch_y
+        batch_x_pad = self.pad(batch_x)
+        if output_length:
+            seq_len = [len(x) for x in batch_x]
+            return batch_x_pad, batch_y, seq_len
+        else:
+            return batch_x_pad, batch_y
 
     @staticmethod
     def pad(batch, fill=0):
@@ -245,7 +250,10 @@ class ToyTrainer(BaseTrainer):
         return data_train, data_dev, 0, 1
 
     def mode(self, test=False):
-        self.model.mode(test)
+        if test:
+            self.model.eval()
+        else:
+            self.model.train()
 
     def data_forward(self, network, x):
         return network(x)
@@ -333,7 +341,7 @@ class POSTrainer(BaseTrainer):
         return loss
 
     def best_eval_result(self, validator):
-        loss, accuracy = validator.matrices()
+        loss, accuracy = validator.metrics()
         if accuracy > self.best_accuracy:
             self.best_accuracy = accuracy
             return True
diff --git a/fastNLP/loader/dataset_loader.py b/fastNLP/loader/dataset_loader.py
index 65daafed..dc5640f1 100644
--- a/fastNLP/loader/dataset_loader.py
+++ b/fastNLP/loader/dataset_loader.py
@@ -11,8 +11,24 @@ class DatasetLoader(BaseLoader):
 
 
 class POSDatasetLoader(DatasetLoader):
-    """loader for pos data sets"""
-
+    """Dataset Loader for POS Tag datasets.
+
+    In these datasets, each line are divided by '\t'
+    while the first Col is the vocabulary and the second
+    Col is the label.
+        Different sentence are divided by an empty line.
+        e.g:
+        Tom label1
+        and label2
+        Jerry   label1
+        .   label3
+        Hello   label4
+        world   label5
+        !   label3
+        In this file, there are two sentence "Tom and Jerry ."
+    and "Hello world !". Each word has its own label from label1
+    to label5.
+    """
     def __init__(self, data_name, data_path):
         super(POSDatasetLoader, self).__init__(data_name, data_path)
 
@@ -23,10 +39,42 @@ class POSDatasetLoader(DatasetLoader):
         return line
 
     def load_lines(self):
-        assert (os.path.exists(self.data_path))
+        """
+        :return data: three-level list
+            [
+                [ [word_11, word_12, ...], [label_1, label_1, ...] ],
+                [ [word_21, word_22, ...], [label_2, label_1, ...] ],
+                ...
+            ]
+        """
         with open(self.data_path, "r", encoding="utf-8") as f:
             lines = f.readlines()
-        return lines
+        return self.parse(lines)
+
+    @staticmethod
+    def parse(lines):
+        data = []
+        sentence = []
+        for line in lines:
+            line = line.strip()
+            if len(line) > 1:
+                sentence.append(line.split('\t'))
+            else:
+                words = []
+                labels = []
+                for tokens in sentence:
+                    words.append(tokens[0])
+                    labels.append(tokens[1])
+                data.append([words, labels])
+                sentence = []
+        if len(sentence) != 0:
+            words = []
+            labels = []
+            for tokens in sentence:
+                words.append(tokens[0])
+                labels.append(tokens[1])
+            data.append([words, labels])
+        return data
 
 
 class ClassDatasetLoader(DatasetLoader):
@@ -112,3 +160,10 @@ class LMDatasetLoader(DatasetLoader):
         with open(self.data_path, "r", encoding="utf=8") as f:
             text = " ".join(f.readlines())
         return text.strip().split()
+
+
+if __name__ == "__main__":
+    data = POSDatasetLoader("xxx", "../../test/data_for_tests/people.txt").load_lines()
+    for example in data:
+        for w, l in zip(example[0], example[1]):
+            print(w, l)
diff --git a/fastNLP/loader/preprocess.py b/fastNLP/loader/preprocess.py
index ee5524d3..7cd91f9c 100644
--- a/fastNLP/loader/preprocess.py
+++ b/fastNLP/loader/preprocess.py
@@ -7,6 +7,10 @@ DEFAULT_RESERVED_LABEL = ['<reserved-2>',
                           '<reserved-3>',
                           '<reserved-4>']  # dict index = 2~4
 
+DEFAULT_WORD_TO_INDEX = {DEFAULT_PADDING_LABEL: 0, DEFAULT_UNKNOWN_LABEL: 1,
+                         DEFAULT_RESERVED_LABEL[0]: 2, DEFAULT_RESERVED_LABEL[1]: 3,
+                         DEFAULT_RESERVED_LABEL[2]: 4}
+
 
 # the first vocab in dict with the index = 5
 
@@ -24,69 +28,86 @@ class BasePreprocess(object):
 class POSPreprocess(BasePreprocess):
     """
         This class are used to preprocess the pos datasets.
-        In these datasets, each line are divided by '\t'
-    while the first Col is the vocabulary and the second
-    Col is the label.
-        Different sentence are divided by an empty line.
-        e.g:
-        Tom label1
-        and label2
-        Jerry   label1
-        .   label3
-        Hello   label4
-        world   label5
-        !   label3
-        In this file, there are two sentence "Tom and Jerry ."
-    and "Hello world !". Each word has its own label from label1
-    to label5.
-    """
 
+    """
 
-    def __init__(self, data, pickle_path):
+    def __init__(self, data, pickle_path="./", train_dev_split=0):
+        """
+        Preprocess pipeline, including building mapping from words to index, from index to words,
+        from labels/classes to index, from index to labels/classes.
+        :param data: three-level list
+            [
+                [ [word_11, word_12, ...], [label_1, label_1, ...] ],
+                [ [word_21, word_22, ...], [label_2, label_1, ...] ],
+                ...
+            ]
+        :param pickle_path: str, the directory to the pickle files. Default: "./"
+        :param train_dev_split: float in [0, 1]. The ratio of dev data split from training data. Default: 0.
+
+        To do:
+        1. simplify __init__
+        """
         super(POSPreprocess, self).__init__(data, pickle_path)
-        self.word_dict = {DEFAULT_PADDING_LABEL: 0, DEFAULT_UNKNOWN_LABEL: 1,
-                          DEFAULT_RESERVED_LABEL[0]: 2, DEFAULT_RESERVED_LABEL[1]: 3,
-                          DEFAULT_RESERVED_LABEL[2]: 4}
 
-        self.label_dict = None
-        self.data = data
         self.pickle_path = pickle_path
 
-        self.build_dict(data)
-        if not self.pickle_exist("word2id.pkl"):
-            self.word_dict.update(self.word2id(data))
-            file_name = os.path.join(self.pickle_path, "word2id.pkl")
-            with open(file_name, "wb") as f:
-                _pickle.dump(self.word_dict, f)
+        if self.pickle_exist("word2id.pkl"):
+            # load word2index because the construction of the following objects needs it
+            with open(os.path.join(self.pickle_path, "word2id.pkl"), "rb") as f:
+                self.word2index = _pickle.load(f)
+        else:
+            self.word2index, self.label2index = self.build_dict(data)
+            with open(os.path.join(self.pickle_path, "word2id.pkl"), "wb") as f:
+                _pickle.dump(self.word2index, f)
 
-        self.vocab_size = self.id2word()
-        self.class2id()
-        self.num_classes = self.id2class()
-        self.embedding()
-        self.data_train()
-        self.data_dev()
-        self.data_test()
+        if self.pickle_exist("class2id.pkl"):
+            with open(os.path.join(self.pickle_path, "class2id.pkl"), "rb") as f:
+                self.label2index = _pickle.load(f)
+        else:
+            with open(os.path.join(self.pickle_path, "class2id.pkl"), "wb") as f:
+                _pickle.dump(self.label2index, f)
+            #something will be wrong if word2id.pkl is found but class2id.pkl is not found
+
+        if not self.pickle_exist("id2word.pkl"):
+            index2word = self.build_reverse_dict(self.word2index)
+            with open(os.path.join(self.pickle_path, "id2word.pkl"), "wb") as f:
+                _pickle.dump(index2word, f)
+
+        if not self.pickle_exist("id2class.pkl"):
+            index2label = self.build_reverse_dict(self.label2index)
+            with open(os.path.join(self.pickle_path, "word2id.pkl"), "wb") as f:
+                _pickle.dump(index2label, f)
+
+        if not self.pickle_exist("data_train.pkl"):
+            data_train = self.to_index(data)
+            if train_dev_split > 0 and not self.pickle_exist("data_dev.pkl"):
+                data_dev = data_train[: int(len(data_train) * train_dev_split)]
+                with open(os.path.join(self.pickle_path, "data_dev.pkl"), "wb") as f:
+                    _pickle.dump(data_dev, f)
+            with open(os.path.join(self.pickle_path, "data_train.pkl"), "wb") as f:
+                _pickle.dump(data_train, f)
 
     def build_dict(self, data):
         """
         Add new words with indices into self.word_dict, new labels with indices into self.label_dict.
-        :param data: list of list [word, label]
+        :param data: three-level list
+            [
+                [ [word_11, word_12, ...], [label_1, label_1, ...] ],
+                [ [word_21, word_22, ...], [label_2, label_1, ...] ],
+                ...
+            ]
+        :return word2index: dict of {str, int}
+                label2index: dict of {str, int}
         """
-
-        self.label_dict = {}
-        for line in data:
-            line = line.strip()
-            if len(line) <= 1:
-                continue
-            tokens = line.split('\t')
-
-            if tokens[0] not in self.word_dict:
-                # add (word, index) into the dict
-                self.word_dict[tokens[0]] = len(self.word_dict)
-
-            # for label in tokens[1: ]:
-            if tokens[1] not in self.label_dict:
-                self.label_dict[tokens[1]] = len(self.label_dict)
+        label2index = {}
+        word2index = DEFAULT_WORD_TO_INDEX
+        for example in data:
+            for word, label in zip(example[0], example[1]):
+                if word not in word2index:
+                    word2index[word] = len(word2index)
+                if label not in label2index:
+                    label2index[label] = len(label2index)
+        return word2index, label2index
 
     def pickle_exist(self, pickle_name):
         """
@@ -101,90 +122,38 @@ class POSPreprocess(BasePreprocess):
         else:
             return False
 
-    def word2id(self):
-        if self.pickle_exist("word2id.pkl"):
-            return
-        # nothing will be done if word2id.pkl exists
-
-        file_name = os.path.join(self.pickle_path, "word2id.pkl")
-        with open(file_name, "wb") as f:
-            _pickle.dump(self.word_dict, f)
-
-    def id2word(self):
-        if self.pickle_exist("id2word.pkl"):
-            file_name = os.path.join(self.pickle_path, "id2word.pkl")
-            id2word_dict = _pickle.load(open(file_name, "rb"))
-            return len(id2word_dict)
-        # nothing will be done if id2word.pkl exists
+    def build_reverse_dict(self, word_dict):
+        id2word = {word_dict[w]: w for w in word_dict}
+        return id2word
 
-        id2word_dict = {}
-        for word in self.word_dict:
-            id2word_dict[self.word_dict[word]] = word
-        file_name = os.path.join(self.pickle_path, "id2word.pkl")
-        with open(file_name, "wb") as f:
-            _pickle.dump(id2word_dict, f)
-        return len(id2word_dict)
-
-    def class2id(self):
-        if self.pickle_exist("class2id.pkl"):
-            return
-        # nothing will be done if class2id.pkl exists
-
-        file_name = os.path.join(self.pickle_path, "class2id.pkl")
-        with open(file_name, "wb") as f:
-            _pickle.dump(self.label_dict, f)
-
-    def id2class(self):
-        if self.pickle_exist("id2class.pkl"):
-            file_name = os.path.join(self.pickle_path, "id2class.pkl")
-            id2class_dict = _pickle.load(open(file_name, "rb"))
-            return len(id2class_dict)
-        # nothing will be done if id2class.pkl exists
-
-        id2class_dict = {}
-        for label in self.label_dict:
-            id2class_dict[self.label_dict[label]] = label
-        file_name = os.path.join(self.pickle_path, "id2class.pkl")
-        with open(file_name, "wb") as f:
-            _pickle.dump(id2class_dict, f)
-        return len(id2class_dict)
-
-    def embedding(self):
-        if self.pickle_exist("embedding.pkl"):
-            return
-        # nothing will be done if embedding.pkl exists
-
-    def data_train(self):
-        if self.pickle_exist("data_train.pkl"):
-            return
-        # nothing will be done if data_train.pkl exists
-
-        data_train = []
-        sentence = []
-        for w in self.data:
-            w = w.strip()
-            if len(w) <= 1:
-                wid = []
-                lid = []
-                for i in range(len(sentence)):
-                    # if sentence[i][0]=="":
-                    #     print("")
-                    wid.append(self.word_dict[sentence[i][0]])
-                    lid.append(self.label_dict[sentence[i][1]])
-                data_train.append((wid, lid))
-                sentence = []
-                continue
-            sentence.append(w.split('\t'))
-
-        file_name = os.path.join(self.pickle_path, "data_train.pkl")
-        with open(file_name, "wb") as f:
-            _pickle.dump(data_train, f)
-
-    def data_dev(self):
-        pass
-
-    def data_test(self):
-        pass
+    def to_index(self, data):
+        """
+        Convert word strings and label strings into indices.
+        :param data: three-level list
+            [
+                [ [word_11, word_12, ...], [label_1, label_1, ...] ],
+                [ [word_21, word_22, ...], [label_2, label_1, ...] ],
+                ...
+            ]
+        :return data_index: the shape of data, but each string is replaced by its corresponding index
+        """
+        data_index = []
+        for example in data:
+            word_list = []
+            label_list = []
+            for word, label in zip(example[0], example[1]):
+                word_list.append(self.word2index[word])
+                label_list.append(self.label2index[label])
+            data_index.append([word_list, label_list])
+        return data_index
+
+    @property
+    def vocab_size(self):
+        return len(self.word2index)
+
+    @property
+    def num_classes(self):
+        return len(self.label2index)
 
 
 class ClassPreprocess(BasePreprocess):
diff --git a/fastNLP/modules/aggregation/kmax_pool.py b/fastNLP/modules/aggregation/kmax_pool.py
index 17fa9248..4d71130e 100644
--- a/fastNLP/modules/aggregation/kmax_pool.py
+++ b/fastNLP/modules/aggregation/kmax_pool.py
@@ -9,7 +9,7 @@ import torch.nn as nn
 class KMaxPool(nn.Module):
     """K max-pooling module."""
 
-    def __init__(self, k):
+    def __init__(self, k=1):
         super(KMaxPool, self).__init__()
         self.k = k
 
diff --git a/fastNLP/modules/aggregation/linear_attention.py b/fastNLP/modules/aggregation/linear_attention.py
deleted file mode 100644
index 8f761c7a..00000000
--- a/fastNLP/modules/aggregation/linear_attention.py
+++ /dev/null
@@ -1,9 +0,0 @@
-from fastNLP.modules.aggregation.attention import Attention
-
-
-class LinearAttention(Attention):
-    def __init__(self, normalize=False):
-        super(LinearAttention, self).__init__(normalize)
-
-    def _atten_forward(self, query, memory):
-        raise NotImplementedError
diff --git a/fastNLP/modules/aggregation/self_attention.py b/fastNLP/modules/aggregation/self_attention.py
index f3581b44..aeaef4db 100644
--- a/fastNLP/modules/aggregation/self_attention.py
+++ b/fastNLP/modules/aggregation/self_attention.py
@@ -8,14 +8,15 @@ class SelfAttention(nn.Module):
     Self Attention Module.
 
     Args:
-    input_size : the size for the input vector
-    d_a : the width of weight matrix
-    r : the number of encoded vectors
+    input_size: int, the size for the input vector
+    dim: int, the width of weight matrix.
+    num_vec: int, the number of encoded vectors
     """
-    def __init__(self, input_size, d_a, r):
+
+    def __init__(self, input_size, dim=10, num_vec=10):
         super(SelfAttention, self).__init__()
-        self.W_s1 = nn.Parameter(torch.randn(d_a, input_size), requires_grad=True)
-        self.W_s2 = nn.Parameter(torch.randn(r, d_a), requires_grad=True)
+        self.W_s1 = nn.Parameter(torch.randn(dim, input_size), requires_grad=True)
+        self.W_s2 = nn.Parameter(torch.randn(num_vec, dim), requires_grad=True)
         self.softmax = nn.Softmax(dim=2)
         self.tanh = nn.Tanh()
 
diff --git a/fastNLP/modules/encoder/char_embedding.py b/fastNLP/modules/encoder/char_embedding.py
index ba70445b..72680e5b 100644
--- a/fastNLP/modules/encoder/char_embedding.py
+++ b/fastNLP/modules/encoder/char_embedding.py
@@ -5,13 +5,15 @@ from torch import nn
 
 class ConvCharEmbedding(nn.Module):
 
-    def __init__(self, char_emb_size, feature_maps=(40, 30, 30), kernels=(3, 4, 5)):
+    def __init__(self, char_emb_size=50, feature_maps=(40, 30, 30), kernels=(3, 4, 5)):
         """
         Character Level Word Embedding
-        :param char_emb_size: the size of character level embedding,
+        :param char_emb_size: the size of character level embedding. Default: 50
             say 26 characters, each embedded to 50 dim vector, then the input_size is 50.
-        :param feature_maps: table of feature maps (for each kernel width)
-        :param kernels: table of kernel widths
+        :param feature_maps: tuple of int. The length of the tuple is the number of convolution operations
+            over characters. The i-th integer is the number of filters (dim of out channels) for the i-th
+            convolution.
+        :param kernels: tuple of int. The width of each kernel.
         """
         super(ConvCharEmbedding, self).__init__()
         self.convs = nn.ModuleList([
@@ -23,29 +25,35 @@ class ConvCharEmbedding(nn.Module):
         :param x: [batch_size * sent_length, word_length, char_emb_size]
         :return: [batch_size * sent_length, sum(feature_maps), 1]
         """
-        x = x.contiguous().view(x.size(0), 1, x.size(1), x.size(2))  # [batch_size*sent_length, channel, width, height]
-        x = x.transpose(2, 3)  # [batch_size*sent_length, channel, height, width]
+        x = x.contiguous().view(x.size(0), 1, x.size(1), x.size(2))
+        # [batch_size*sent_length, channel, width, height]
+        x = x.transpose(2, 3)
+        # [batch_size*sent_length, channel, height, width]
         return self.convolute(x).unsqueeze(2)
 
     def convolute(self, x):
         feats = []
         for conv in self.convs:
-            y = conv(x)  # [batch_size*sent_length, feature_maps[i], 1, width - kernels[i] + 1]
-            y = torch.squeeze(y, 2)  # [batch_size*sent_length, feature_maps[i], width - kernels[i] + 1]
+            y = conv(x)
+            # [batch_size*sent_length, feature_maps[i], 1, width - kernels[i] + 1]
+            y = torch.squeeze(y, 2)
+            # [batch_size*sent_length, feature_maps[i], width - kernels[i] + 1]
             y = F.tanh(y)
-            y, __ = torch.max(y, 2)  # [batch_size*sent_length, feature_maps[i]]
+            y, __ = torch.max(y, 2)
+            # [batch_size*sent_length, feature_maps[i]]
             feats.append(y)
         return torch.cat(feats, 1)  # [batch_size*sent_length, sum(feature_maps)]
 
 
 class LSTMCharEmbedding(nn.Module):
     """
-    Character Level Word Embedding with LSTM
-    :param char_emb_size: the size of character level embedding,
+    Character Level Word Embedding with LSTM with a single layer.
+    :param char_emb_size: int, the size of character level embedding. Default: 50
         say 26 characters, each embedded to 50 dim vector, then the input_size is 50.
+    :param hidden_size: int, the number of hidden units. Default:  equal to char_emb_size.
     """
 
-    def __init__(self, char_emb_size, hidden_size=None):
+    def __init__(self, char_emb_size=50, hidden_size=None):
         super(LSTMCharEmbedding, self).__init__()
         self.hidden_size = char_emb_size if hidden_size is None else hidden_size
 
diff --git a/fastNLP/modules/encoder/conv.py b/fastNLP/modules/encoder/conv.py
index a3a572d9..1aeedbd5 100644
--- a/fastNLP/modules/encoder/conv.py
+++ b/fastNLP/modules/encoder/conv.py
@@ -2,12 +2,14 @@
 # encoding: utf-8
 
 import torch.nn as nn
+from torch.nn.init import xavier_uniform
 # import torch.nn.functional as F
 
 
 class Conv(nn.Module):
     """
     Basic 1-d convolution module.
+    initialize with xavier_uniform
     """
 
     def __init__(self, in_channels, out_channels, kernel_size,
@@ -23,6 +25,7 @@ class Conv(nn.Module):
             dilation=dilation,
             groups=groups,
             bias=bias)
+        xavier_uniform(self.conv.weight)
 
     def forward(self, x):
         return self.conv(x)  # [N,C,L]
diff --git a/fastNLP/modules/encoder/embedding.py b/fastNLP/modules/encoder/embedding.py
index 17c8f20a..1e11adfe 100644
--- a/fastNLP/modules/encoder/embedding.py
+++ b/fastNLP/modules/encoder/embedding.py
@@ -7,12 +7,13 @@ class Lookuptable(nn.Module):
 
     Args:
     nums : the size of the lookup table
-    dims : the size of each vector
+    dims : the size of each vector. Default: 50.
     padding_idx : pads the tensor with zeros whenever it encounters this index
     sparse : If True, gradient matrix will be a sparse tensor. In this case,
     only optim.SGD(cuda and cpu) and optim.Adagrad(cpu) can be used
     """
-    def __init__(self, nums, dims, padding_idx=0, sparse=False):
+
+    def __init__(self, nums, dims=50, padding_idx=0, sparse=False):
         super(Lookuptable, self).__init__()
         self.embed = nn.Embedding(nums, dims, padding_idx, sparse=sparse)
         
diff --git a/fastNLP/modules/encoder/lstm.py b/fastNLP/modules/encoder/lstm.py
index 6d110fca..2d8c14f4 100644
--- a/fastNLP/modules/encoder/lstm.py
+++ b/fastNLP/modules/encoder/lstm.py
@@ -8,11 +8,12 @@ class Lstm(nn.Module):
     Args:
     input_size : input size
     hidden_size : hidden size
-    num_layers : number of hidden layers
-    dropout : dropout rate
-    bidirectional : If True, becomes a bidirectional RNN
+    num_layers : number of hidden layers. Default: 1
+    dropout : dropout rate. Default: 0.5
+    bidirectional : If True, becomes a bidirectional RNN. Default: False.
     """
-    def __init__(self, input_size, hidden_size, num_layers, dropout, bidirectional):
+
+    def __init__(self, input_size, hidden_size, num_layers=1, dropout=0.5, bidirectional=False):
         super(Lstm, self).__init__()
         self.lstm = nn.LSTM(input_size, hidden_size, num_layers, bias=True, batch_first=True,
                             dropout=dropout, bidirectional=bidirectional)
diff --git a/test/test_loader.py b/test/test_loader.py
index 58e5dfe5..b18a2fcf 100644
--- a/test/test_loader.py
+++ b/test/test_loader.py
@@ -1,9 +1,23 @@
 import unittest
 
+from fastNLP.loader.dataset_loader import POSDatasetLoader
 
-class MyTestCase(unittest.TestCase):
-    def test_something(self):
-        self.assertEqual(True, False)
+
+class TestPreprocess(unittest.TestCase):
+    def test_case_1(self):
+        data = [[["Tom", "and", "Jerry", "."], ["T", "F", "T", "F"]],
+                ["Hello", "world", "!"], ["T", "F", "F"]]
+        pickle_path = "./data_for_tests/"
+        # POSPreprocess(data, pickle_path)
+
+
+class TestDatasetLoader(unittest.TestCase):
+    def test_case_1(self):
+        data = """Tom\tT\nand\tF\nJerry\tT\n.\tF\n\nHello\tT\nworld\tF\n!\tF"""
+        lines = data.split("\n")
+        answer = POSDatasetLoader.parse(lines)
+        truth = [[["Tom", "and", "Jerry", "."], ["T", "F", "T", "F"]], [["Hello", "world", "!"], ["T", "F", "F"]]]
+        self.assertListEqual(answer, truth, "POS Dataset Loader")
 
 
 if __name__ == '__main__':