bpo-43682: @staticmethod inherits attributes

[vstinner]

Static methods (@staticmethod) and class methods (@classmethod) now
inherit the method attributes (module, name, qualname,
doc, annotations) and have a new wrapped attribute.

Changes:

• Add a repr() method to staticmethod and classmethod types.
• Add tests on the @classmethod decorator.

https://bugs.python.org/issue43682

[vstinner]

functools_wraps() call in cm_init() failed because Python didn't initialize PyClassMethod_Type type at startup. I created https://bugs.python.org/issue43770 to fix the issue: it's now fixed by df5dc1c

[vstinner]

I chose the following representation:

$ ./python -q
>>> def func(): pass
... 
>>> staticmethod(func)
<staticmethod(<function func at 0x7f39e8152c50>)>
>>> classmethod(func)
<classmethod(<function func at 0x7f39e8152c50>)>

[vstinner]

cc @serhiy-storchaka

[geryogam]

@vstinner What’s this new __wrapped__ attribute? Is it the same as the existing __func__ attribute? If so, why did you introduce it?

[carljm]

What’s this new __wrapped__ attribute? Is it the same as the existing __func__ attribute? If so, why did you introduce it?

It's a standard attribute added by functools.wraps to wrapper functions allowing unwrapping back to the wrapped function (eg by inspect.unwrap). So it's generally useful for wrappers to set it.

[geryogam]

@carljm Thanks, so I guess in this case it’s a documented duplicate of __func__ which is an undocumented attribute.

[serhiy-storchaka]

It is better to use _PyObject_LookupAttr() here. See #106303.