[issue2319] abc.py:ABCMeta.__instancecheck__ broken for old style classes

[Ralf Schmitt]

New submission from Ralf Schmitt <schmir at gmail.com>:

The following short program raises an exception:

import UserList

class C:
    pass
   
print isinstance(C, UserList.UserList)

---------
exception:
Traceback (most recent call last):
  File "t.py", line 6, in <module>
    print isinstance(C, UserList.UserList)
  File "/home/ralf/py26/lib/python2.6/abc.py", line 120, in
__instancecheck__
    subclass = instance.__class__
AttributeError: class C has no attribute '__class__'

If I use a new style class it works.

----------
components: Interpreter Core
messages: 63630
nosy: schmir
severity: normal
status: open
title: abc.py:ABCMeta.__instancecheck__ broken for old style classes
type: crash
versions: Python 2.6

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Tracker <report at bugs.python.org>
<http://bugs.python.org/issue2319>
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