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

Antoine Pitrou solipsis at pitrou.net
Mon Nov 29 00:44:18 CET 2010

On Mon, 29 Nov 2010 00:37:12 +0200
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.

It raises an exception for the same reason that
    1 in 'a'
raises an exception. Because there's no way that an int can belong in a
string, or an int can be a subclass of anything; and so passing an int
there is very likely to be a programming error.

Python is dynamically typed, it doesn't mean it is untyped (contrast
with PHP). If you want arbitrary polymorphism, you have to write the
supporting code yourself.



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