[docs] [issue37203] Correct classmethod emulation in Descriptor HowTo Guide

[Géry]

Géry <gery.ogam at gmail.com> added the comment:

@Raymond Hettinger

> The goal in the descriptor how-to is to give an understanding of how descriptors work.

Okay. So I don't know if that was clear in my last message but that also means replacing the current "Function" implementation:

class Function(object):
    . . .
    def __get__(self, obj, objtype=None):
        "Simulate func_descr_get() in Objects/funcobject.c"
        if obj is None:
            return self
        return types.MethodType(self, obj)

with something like this:

class Function(object):
    . . .
    def __get__(self, obj, objtype=None):
        "Simulate func_descr_get() in Objects/funcobject.c"
        if obj is None:
            return self
        def newfunc(*args, **kwargs):
            return self(obj, *args, **kwargs)
        return newfunc
        # "newfunc" emulates "types.MethodType(self, obj)"

And as you said, adding a similar comment to the "ClassMethod" implementation (and **kwargs):

class ClassMethod(object):
    "Emulate PyClassMethod_Type() in Objects/funcobject.c"

    def __init__(self, f):
        self.f = f

    def __get__(self, obj, klass=None):
        if klass is None:
            klass = type(obj)
        def newfunc(*args, **kwargs):
            return self.f(klass, *args, **kwargs)
        return newfunc
        # "newfunc" emulates "types.MethodType(self.f, klass)"

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37203>
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