diff --git a/fastNLP/core/dataset.py b/fastNLP/core/dataset.py
index 131ba28d..18da9bd7 100644
--- a/fastNLP/core/dataset.py
+++ b/fastNLP/core/dataset.py
@@ -33,7 +33,9 @@ class DataSet(object):
             return self.dataset[name][self.idx]
 
         def __setitem__(self, name, val):
-            # TODO check new field.
+            if name not in self.dataset:
+                new_fields = [None]*len(self.dataset)
+                self.dataset.add_field(name, new_fields)
             self.dataset[name][self.idx] = val
 
         def __repr__(self):
@@ -45,6 +47,9 @@ class DataSet(object):
         if instance is not None:
             self._convert_ins(instance)
 
+    def __contains__(self, item):
+        return item in self.field_arrays
+
     def __iter__(self):
         return self.DataSetIter(self)
 
diff --git a/reproduction/chinese_word_segment/process/cws_processor.py b/reproduction/chinese_word_segment/process/cws_processor.py
index bb76b974..3e6b9c3b 100644
--- a/reproduction/chinese_word_segment/process/cws_processor.py
+++ b/reproduction/chinese_word_segment/process/cws_processor.py
@@ -7,7 +7,7 @@ from fastNLP.core.vocabulary import Vocabulary
 from fastNLP.core.dataset import DataSet
 
 from fastNLP.api.processor import Processor
-
+from reproduction.chinese_word_segment.process.span_converter import *
 
 _SPECIAL_TAG_PATTERN = '<[a-zA-Z]+>'
 
diff --git a/reproduction/chinese_word_segment/process/span_converter.py b/reproduction/chinese_word_segment/process/span_converter.py
index 23e590c4..2635df0e 100644
--- a/reproduction/chinese_word_segment/process/span_converter.py
+++ b/reproduction/chinese_word_segment/process/span_converter.py
@@ -2,9 +2,9 @@
 import re
 
 
-class SpanConverterBase:
+class SpanConverter:
     def __init__(self, replace_tag, pattern):
-        super(SpanConverterBase, self).__init__()
+        super(SpanConverter, self).__init__()
 
         self.replace_tag = replace_tag
         self.pattern = pattern
@@ -33,7 +33,7 @@ class SpanConverterBase:
         return spans
 
 
-class AlphaSpanConverter(SpanConverterBase):
+class AlphaSpanConverter(SpanConverter):
     def __init__(self):
         replace_tag = '<ALPHA>'
         # 理想状态下仅处理纯为字母的情况, 但不处理<[a-zA-Z]+>(因为这应该是特殊的tag).
@@ -42,7 +42,7 @@ class AlphaSpanConverter(SpanConverterBase):
         super(AlphaSpanConverter, self).__init__(replace_tag, pattern)
 
 
-class DigitSpanConverter(SpanConverterBase):
+class DigitSpanConverter(SpanConverter):
     def __init__(self):
         replace_tag = '<NUM>'
         pattern = '\d[\d\\.]*(?=[\u4e00-\u9fff  ,%.!<-])'
@@ -71,7 +71,7 @@ class DigitSpanConverter(SpanConverterBase):
             return '<NUM>'
 
 
-class TimeConverter(SpanConverterBase):
+class TimeConverter(SpanConverter):
     def __init__(self):
         replace_tag = '<TOC>'
         pattern = '\d+[:：∶][\d:：∶]+(?=[\u4e00-\u9fff  ,%.!<-])'
@@ -80,7 +80,7 @@ class TimeConverter(SpanConverterBase):
 
 
 
-class MixNumAlphaConverter(SpanConverterBase):
+class MixNumAlphaConverter(SpanConverter):
     def __init__(self):
         replace_tag = '<MIX>'
         pattern = None
@@ -177,7 +177,7 @@ class MixNumAlphaConverter(SpanConverterBase):
 
 
 
-class EmailConverter(SpanConverterBase):
+class EmailConverter(SpanConverter):
     def __init__(self):
         replaced_tag = "<EML>"
         pattern = '[0-9a-zA-Z]+[@][.﹒0-9a-zA-Z@]+(?=[\u4e00-\u9fff  ,%.!<\\-"$])'