[Python-Dev] PEP 362 minor nits

Wed Jun 20 15:01:23 CEST 2012

On 2012年06月20日, 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)
-
Yury