[Patches] [ python-Patches-1708353 ] Make isinstance/issubclass overloadable

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Patches item #1708353, was opened at 2007-04-26 16:16
Message generated for change (Comment added) made by gvanrossum
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Category: Core (C code)
Group: Python 3000
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Guido van Rossum (gvanrossum)
Assigned to: Guido van Rossum (gvanrossum)
Summary: Make isinstance/issubclass overloadable

Initial Comment:
I came up with a fairly simple way to overload isinstance() and issubclass().  The class that is the second argument can define a (class) method named __instancecheck__ or __subclasscheck__ which, if present, will be called *instead* of the normal approach.

The names are different to remind users that the calling convention is the opposite -- isinstance(x, C) maps to C.__instancecheck__(x).


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>Comment By: Guido van Rossum (gvanrossum)
Date: 2007-04-26 16:34

Message:
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Oops, forget the first attempt; isinstance(Integer(), Integer) would be
False!  Now it's True, and more tests are added.
File Added: typechecks.diff

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You can respond by visiting: 
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