This simple test case results in a lib2to3 crash with an AssertionError in 2.7.11


source = '''

class Test(object):

    tests = []


'''

from lib2to3.refactor import RefactoringTool


def main():
    tool = RefactoringTool([])
    tool.refactor_string(source, '')

        
Exception:

Traceback (most recent call last):
  File "test.py", line 21, in <module>
    main()
  File "test.py", line 16, in main
    tool.refactor_string(source, '')
  File "c:\Python27\Lib\lib2to3\refactor.py", line 380, in refactor_string
    name, err.__class__.__name__, err)
  File "c:\Python27\Lib\lib2to3\refactor.py", line 377, in refactor_string
    tree = self.driver.parse_string(data)
  File "c:\Python27\Lib\lib2to3\pgen2\driver.py", line 106, in parse_string
    return self.parse_tokens(tokens, debug)
  File "c:\Python27\Lib\lib2to3\pgen2\driver.py", line 71, in parse_tokens
    if p.addtoken(type, value, (prefix, start)):
  File "c:\Python27\Lib\lib2to3\pgen2\parse.py", line 127, in addtoken
    assert t < 256
AssertionError

Pretty weird: A manually built Python 2.7.11 with VS 2008 doesn't show this issue.