[Python-Dev] PEP 362 minor nits (original) (raw)

Yury Selivanov yselivanov.ml at gmail.com
Wed Jun 20 15:01:23 CEST 2012

On 2012-06-20, at 4:30 AM, Steven D'Aprano wrote:

On Tue, Jun 19, 2012 at 08:11:26PM -0400, Yury Selivanov wrote:

So using the signature will be OK for 'Foo.bar' and 'Foo().bar', but not for 'Foo.dict['bar']' - which I think is fine (since staticmethod & classmethod instances are not callable) There has been some talk on Python-ideas about making staticmethod and classmethod instances callable. Speaking of non-instance method descriptors, please excuse this silly question, I haven't quite understood the implementation well enough to answer this question myself. Is there anything needed to make signature() work correctly with custom method-like descriptors such as this? http://code.activestate.com/recipes/577030-dualmethod-descriptor

Well, as Nick said -- the PEP way is to create a new Signature with a first parameter skipped.

But in this particular case you can rewrite it (I'd say preferred way):

class dualmethod:
    def __init__(self, func):
        self.func = func

    def __get__(self, instance, owner):
        if instance is None:
            return types.MethodType(self.func, owner)
        else:
            return types.MethodType(self.func, instance)

Or another way, using functools.partial:

class dualmethod:
    def __init__(self, func):
        self.func = func

    def __get__(self, instance, owner):
        if instance is None:
            return functools.partial(self.func, owner)
        else:
            return functools.partial(self.func, instance)

Since 'MethodType' and 'partial' are supported by signature(), everything will work automatically (i.e. first argument will be skipped)

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