[Python-ideas] `issubclass` shouldn't be raising exceptions for non-type inputs

cool-RR cool-rr at cool-rr.com
Mon Nov 29 00:23:47 CET 2010

On Mon, Nov 29, 2010 at 1:21 AM, Michael Foord <fuzzyman at voidspace.org.uk>wrote:

> On 28 November 2010 22:37, cool-RR <cool-rr at cool-rr.com> wrote:
>> `issubclass(1, list)` raises an Exception, complaining that `1` is not a
>> class. This is wrong in my opinion. It should just return False.
>> Use case: 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`.
> Unfortunately it would be a backwards incompatible change. Currently
> catching the TypeError from issubclass is a way of detecting that an object
> *isn't* a type.

Who is doing that?! What's wrong with something like `isinstance(thing,
(type, types.ClassType))`?

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