Problematic logical expressions for types.ClassType checks in django.utils.dictconfig

[Stefan Zimmermann]

BaseConfigurator.configure_custom and DictConfigurator.configure_handler both contain the following code:

if not hasattr(c, '__call__') and hasattr(types, 'ClassType') and type(c) != types.ClassType:
    c = self.resolve(c)

The problem is that this logical expression always fails if the types module doesn't have the ClassType attribute (I encountered this when working with the django-3k fork)

The expression could be written like this:

if not hasattr(c, '__call__') and (not hasattr(types, 'ClassType') or type(c) != types.ClassType):
    c = self.resolve(c)

But the hasattr call could also be completely dropped (In python 2.x types.ClassType is always there and 2to3 converts it to type):

if not hasattr(c, '__call__') and type(c) != types.ClassType:
    c = self.resolve(c)

[Aymeric Augustin]

Django's dictconfig is a literal copy of the one in Python 2.7, included verbatim to ensure compatibility across Python versions.

Has this issue been reported and/or fixed in Python's native dictconfig?

If there's a problem with the version bundled with Django, the preferred fix is to update to a new verbatim copy, not to patch Django's version.

[Łukasz Rekucki]

It's a non issue for Python, beacause this code work in Python 2.x, and Python 3.2+ just uses if not callable(c). One way to fix this, without touching the verbatim copy would be to alter 2to3, to fix the check.

I may be missing something, but isn't this check exactly equal to what callable() does? If yes, I'm in favor of changing this.

PS. I wonder what's the story behind this subtle diffrence in what callable() does:

2.x: ​http://hg.python.org/cpython/file/7c263bfc92f5/Objects/object.c#l1650

3.2: ​http://hg.python.org/cpython/file/cd748bab3cdd/Objects/object.c#l1179

[Aymeric Augustin]

This bug was filed against an old experimental port to Python 3 that was abandonned.

Django now attemps to import dictConfig from logging.config, and falls back to importing it from django.utils.dictconfig only on Python 2.6.