[Python-bugs-list] [Bug #124106] isinstance() doesn't *quite* work on ExtensionClasses

[noreply@sourceforge.net]

Bug #124106, was updated on 2000-Dec-01 17:21
Here is a current snapshot of the bug.

Project: Python
Category: Core
Status: Open
Resolution: None
Bug Group: None
Priority: 5
Submitted by: gward
Assigned to : nascheme
Summary: isinstance() doesn't *quite* work on ExtensionClasses

Details: In 1.6, isinstance() and issubclass() were generalized so they work on ExtensionClass instances and classes as well as vanilla Python instances and classes... almost.  Unfortunately, it doesn't work in one case:

  isinstance(inst, ECClass)

where inst is a vanilla Python instance and ECClass an ExtensionClass-derived class raises TypeError with the message "second argument must be a class".

Neil says this should work with his PyInstance_Check() patch, so I'm going to assign this one to him.


Follow-Ups:

Date: 2000-Dec-01 17:23
By: gward

Comment:
Oops, forgot to include this script that demonstrates the bug:

"""
from ExtensionClass import ExtensionClass, Base

class SuperEC (Base):
    pass

class ChildEC (SuperEC):
    pass

class Super:
    pass

class Child (Super):
    pass

def test(cond):
    print cond and "ok" or "not ok"

c1 = Child()
c2 = ChildEC()

test(issubclass(Child, Super))
test(issubclass(ChildEC, SuperEC))

test(isinstance(c1, Child))
test(isinstance(c1, Super))
test(not isinstance(c2, Child))
test(isinstance(c2, ChildEC))
test(isinstance(c2, SuperEC))

test(not isinstance(c1, ChildEC))
test(not isinstance(c1, SuperEC))
"""

When I run this, I get the following output:
"""
ok
ok
ok
ok
ok
ok
ok
Traceback (most recent call last):
  File "ectest", line 30, in ?
    test(not isinstance(c1, ChildEC))
TypeError: second argument must be a class
"""

Output is the same with Python 1.6 and 2.0.

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http://sourceforge.net/bugs/?func=detailbug&bug_id=124106&group_id=5470