[Python-bugs-list] [ python-Bugs-467267 ] isinstance depends on import form

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Bugs item #467267, was opened at 2001-10-02 11:56
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http://sourceforge.net/tracker/?func=detail&atid=105470&aid=467267&group_id=5470

Category: Python Interpreter Core
Group: Python 2.1.1
Status: Open
Resolution: None
Priority: 5
Submitted By: Luis P Caamano (lcaamano)
Assigned to: Nobody/Anonymous (nobody)
Summary: isinstance depends on import form

Initial Comment:
isinstance(obj, cls) fails if cls is in a package and 
the import line of the obj creator is different from 
the import line in the code calling isinstance.

It seems to me that the problem is the address test in 
PyObject_IsInstance(), because different import forms 
produce objects with different addresses.

A limited workaround would be to test for class name 
but that doesn't include subclasses or types.  So, 
instead of:

if isinstance(obj, class):

use

if obj.__class__.__name__ == 'classname':

-------Sample--------------------

Python 2.1.1 (#2, Jul 25 2001, 17:54:11) 
[GCC 2.96 20000731 (Red Hat Linux 7.1 2.96-81)] on 
linux2
Type "copyright", "credits" or "license" for more 
information.
>>> from spam.eggs import SpamAndEggs
>>> import spam.eggs
>>> '0x%x' % id(spam.eggs.SpamAndEggs)
'0x8161ce4'
>>> '0x%x' % id(SpamAndEggs)
'0x814c29c'
>>> sag = spam.eggs.SpamAndEggs()
>>> isinstance(sag, SpamAndEggs)
0
>>> isinstance(sag, spam.eggs.SpamAndEggs)
1
>>> sag.__class__
<class spam.eggs.SpamAndEggs at 0x8161ce4>
>>> sag.__class__.__name__
'SpamAndEggs'
>>> SpamAndEggs.__name__
'SpamAndEggs'
>>> spam.eggs.SpamAndEggs.__name__
'SpamAndEggs'
>>> 


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