annoying doctest problem

[gordianknot1981 at gmail.com]

#!/usr/bin/python
# -*- coding: utf-8 -*-

import re
kivy_class_ptn      = re.compile(r"<\b[\w_.\@\+]+>:?")


def test_kivy_class(s):
    """
    >>> s = "<MYBT at ToggleButton+Button>:"
    >>> test_kivy_class(s)
    "<MYBT at ToggleButton+Button>:"
    >>> s = "<MYBT>"
    >>> test_kivy_class(s)
    "<MYBT>"
    """
    ret =  re.search(kivy_class_ptn, s)
    if ret: return ret.group()
    else:   return ''




if __name__ == "__main__":

    import doctest
    doctest.testmod()



output:

**********************************************************************
File "F:/MyDocument/[Programing]/Python/PhotoshopAsGui/python3_branch/regexSnippet.py", line 19, in __main__.test_kivy_class
Failed example:
    test_kivy_class(s)
Expected:
    "<MYBT at ToggleButton+Button>:"
Got:
    '<MYBT at ToggleButton+Button>:'
**********************************************************************
File "F:/MyDocument/[Programing]/Python/PhotoshopAsGui/python3_branch/regexSnippet.py", line 22, in __main__.test_kivy_class
Failed example:
    test_kivy_class(s)
Expected:
    "<MYBT>"
Got:
    '<MYBT>'
**********************************************************************
1 items had failures:
   2 of   8 in __main__.test_kivy_class
***Test Failed*** 2 failures.




It failed with an unknown reason that evaluate two expected equal value but got an unexpected result! I'm struggling with this problem for a long time. Did I did something wrong? And how do I to fix it?

any help is appreciated. :)