[Python-bugs-list] [ python-Bugs-467267 ] isinstance depends on import form (original) (raw)

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Tue, 02 Oct 2001 14:01:26 -0700

Bugs item #467267, was opened at 2001-10-02 11:56 You can respond by visiting: 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'

Comment By: Luis P Caamano (lcaamano) Date: 2001-10-02 14:01

Message: Logged In: YES user_id=279987

With the site-packages/pkg1.pth file:

from pkg1.spam.eggs import SpamAndEggs import spam.eggs '0x%x' % id(SpamAndEggs) '0x814e174' '0x%x' % id(spam.eggs.SpamAndEggs) '0x8168fac' import pkg1.spam.eggs '0x%x' % id(pkg1.spam.eggs.SpamAndEggs) '0x814e174'

It is starting to make sense.

-- lpc

Comment By: Luis P Caamano (lcaamano) Date: 2001-10-02 13:34

Message: Logged In: YES user_id=279987

After getting your email I went and rechecked things in site-packages and the only suspicious thing was a .pth file. I removed the .pth file and now I'm getting the same address. I'm still investigating. At this moment I have no idea why I'm getting different objects.

Let me investigate a little bit more and I'll get back to you.

I apologize for not having verified this better.

-- Luis Caamano

Comment By: Guido van Rossum (gvanrossum) Date: 2001-10-02 12:26

Message: Logged In: YES user_id=6380

We need more information: please show all code involved (use the file upload, please check the checkbox or the upload won't work; you must be logged in to SourceForge as yourself).

From the session you post, it seems that there are two distinct SpamAndEggs objects, but without seeing your code it's hard to understand why.

You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=467267&group_id=5470