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

Michael Foord fuzzyman at voidspace.org.uk
Mon Nov 29 00:21:25 CET 2010

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.

Maybe one to chalk up for Python 4...


> Ram.
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