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To: python-list@python.org
From: Christian Heimes <christian@python.org>
Subject: Re: python 3 problem: how to convert an extension method into a class Method
Date: Tue, 26 Feb 2013 22:08:02 +0100
References: <512CEF0C.3020906@chamonix.reportlab.co.uk> <512D18C2.5000802@stoneleaf.us>
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Xref: csiph.com comp.lang.python:40007

Am 26.02.2013 21:19, schrieb Ethan Furman:
> Dumb question, but have you tried just assigning it?  In Py3 methods are
> just normal functions...
> 
> 8<----------------------
>   class A():
>       pass
> 
>   A.method = c_method
> 8<----------------------

That doesn't work with builtin functions because they don't implement
the descriptor protocol:

Python 3.3.0 (v3.3.0:bd8afb90ebf2, Feb  8 2013, 00:38:29)
[GCC 4.7.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> class Example:
...     id = id
...
>>> Example().id()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: id() takes exactly one argument (0 given)

You can use PyInstanceMethod_Type to wrap a builtin method in something
that acts like a normal method. I implemented the type for Python 3000
when I removed the unbound method object. It's not available to pure
Python code except for testing:

>>> import _testcapi
>>> class Example:
...     id = _testcapi.instancemethod(id)
...
>>> Example().id()
140525206026320

The C code is rather simple and small. You can easily re-implement in
Python, too.