>>> import abc
>>> class A(object, metaclass=abc.ABCMeta):
...     pass
>>> issubclass([], A)
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    issubclass([], A)
  File "c:\Python32\lib\abc.py", line 137, in __subclasscheck__
    if subclass in cls._abc_cache:
  File "c:\Python32\lib\_weakrefset.py", line 69, in __contains__
    return ref(item) in self.data
TypeError: cannot create weak reference to 'list' object

I should be able to check whether an object is a subclass of something without confirming it's a type first. I think this call should just return False.

I don't agree. "issubclass(1, list)" has always raised an exception.

But do you think it's a good idea that `issubclass(1, list)` raises an exception? Why not simply return `False`?

Do you think there's someone out there who's counting on `issubclass` to raise an exception?

issubclass is for relationship between classes. Did you consider isinstance() instead?

Amaury, I am aware of what `issubclass` does and what `isinstance` does. I am not manually feeding `[]` into `issubclass`. I have an object which can be either a list, or a string, or a callable, or a type. And I want to check whether it's a sub-class of some base class.

So I don't think I should be taking extra precautions before using `issubclass`: If my object is not a subclass of the given base class, I should just get `False`.

Tell python-ideas about it.

FWIW (which isn't much I guess) it annoys me that I have to protect calls to issubclass with if isinstance(obj, type).