FormEncode验证：单词除以逗号

import formencode

class CommaSepList(formencode.validators.FancyValidator):

    def _to_python(self, value, state):
        return value.split(",")

    def validate_python(self, value, state):
        for elem in value:
            if elem == "": 
                raise formencode.Invalid("an element of the list is empty", value, state) 

>>> CommaSepList.to_python("1,2,3")
['1', '2', '3']
>>> CommaSepList.to_python("1,,")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.5/site-packages/FormEncode-1.2.3dev-py2.5.egg/formencode/api.py", line 416, in to_python
    vp(value, state)
  File "myValidator.py", line 17, in validate_python
    raise formencode.Invalid("an element of the list is empty", value, state)

', '

>>> x = "foo1, bar2, foo3"
>>> x.split(', ')
['foo1', 'bar2', 'foo3']