Issue 765228: Subclassing from Modules (original) (raw)

This issue has been migrated to GitHub: https://github.com/python/cpython/issues/38780

classification

process

Created on 2003-07-03 10:32 by lemburg, last changed 2022-04-10 16:09 by admin. This issue is now closed.

Messages (4)
msg16833 - (view)	Author: Marc-Andre Lemburg (lemburg) *	Date: 2003-07-03 10:32
In Python 2.2.3 there's a problem with accidental subclassing from a Python module, e.g. import MyStuff class A(MyStuff): pass this gives no error until you try to instantiate the class: o = A() TypeError: 'module' object is not callable In Python 2.3 the error is generated at module startup time: class A(MyStuff): pass TypeError: function takes at most 2 arguments (3 given) Since it is rather common that you create modules which have the same name as their most important class, I would find it more appropriate to raise a TypeError with a message "can't subclass a module instance" in both versions.
msg55196 - (view)	Author: Georg Brandl (georg.brandl) *	Date: 2007-08-23 20:07
In 2.5, the message says "module.__init__() takes at most 2 arguments (3 given)", which is at least a bit more specific. You get similar errors when "deriving" from other arbitrary objects, so I don't know if a special case makes sense here.
msg57776 - (view)	Author: Christian Heimes (christian.heimes) *	Date: 2007-11-23 09:02
I agree. Python can't stop the developer from doing stupid things. We could remove Py_TPFLAGS_BASETYPE from the module type but that could cause incompatibilities with existing code. I'm assigning the bug to our beloved dictator to ask for his opinion.
msg57837 - (view)	Author: Guido van Rossum (gvanrossum) *	Date: 2007-11-26 04:16
I don't see an issue to be fixed here; adding special tests in order to provide more detailed error messages is rarely a good idea. Also, PEP 8 has said for years now that modules should *not* be named the same as classes. Yes, there are a few such modules in the standard library. They're historical mistakes that will be fixed in 3.0.