I know how to use @classmethod decorator, but I wonder what does it do internally to the function, which it decorates? How does it take the class/object, on which it is called to pass it as first parameter of the decorated function?
Thanks
2
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3To know what it does internally, you'd need to deep-dive into some C: github.com/python/cpython/blob/… Is that really what you want to know?deceze– deceze ♦2021-05-25 09:04:50 +00:00Commented May 25, 2021 at 9:04
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1Here you can see a Python implementation: gist.github.com/carljm/3004616user2390182– user23901822021-05-25 09:05:11 +00:00Commented May 25, 2021 at 9:05
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1 Answer
@classmethod is a Python descriptor - Python 3, Python 2
You can call decorated method from an object or class.
class Clazz:
@classmethod
def f(arg1):
pass
o = Clazz()
If you call:
o.f(1)
It will be acctually f(type(o), *args) called.
If you call:
Clazz.f(1)
It will be acctually f(Clazz, *args) called.
As in doc, pure-python classmethod would look like:
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):
return self.f(klass, *args)
return newfunc
2 Comments
Gino Mempin
Since Python 2 is now EOL, it would be better to link to Python 3 docs instead: docs.python.org/3/howto/descriptor.html#class-methods
IcyBrk
"@classmethod is a Python descriptor" is not correct, actually @classmethod is a Python decorator, see the documentation reference: docs.python.org/3/library/functions.html#classmethod