python - What magic does staticmethod() do, so that the static method is always called without the instance parameter? -

i trying understand how static methods work internally. know how use @staticmethod decorator avoiding use in post in order dive deeper how static methods work , ask questions.

from know python, if there class a, calling a.foo() calls foo() no arguments whereas calling a().foo() calls foo() 1 argument 1 argument instance a() itself.

however, in case of static methods, seems foo() called no arguments whether call a.foo() or a().foo().

proof below:

>>> class a: ...     x = 'hi' ...     def foo(): ...         print('hello, world') ...     bar = staticmethod(foo) ... >>> a.bar() hello, world >>> a().bar() hello, world >>> a.bar <function a.foo @ 0x00000000005927b8> >>> a().bar <function a.foo @ 0x00000000005927b8> >>> a.bar(1) traceback (most recent call last):   file "<stdin>", line 1, in <module> typeerror: foo() takes 0 positional arguments 1 given >>> a().bar(1) traceback (most recent call last):   file "<stdin>", line 1, in <module> typeerror: foo() takes 0 positional arguments 1 given 

so right in concluding staticmethod() function magic such foo() called 0 arguments?

if define own staticmethod() in own python code, how it? possible define such method our own python code, or can such function defined builtin?

it's implemented descriptor. example:

in [1]: class mystaticmethod(object):    ...:     def __init__(self, func):    ...:         self._func = func    ...:     def __get__(self, inst, cls):    ...:         return self._func    ...:       in [2]: class a(object):    ...:     @mystaticmethod    ...:     def foo():    ...:         print('hello, world!')    ...:           in [3]: a.foo() hello, world!  in [4]: a().foo() hello, world! 

in same way can define classmethod, passing cls original function:

in [5]: functools import partial    ...:     ...: class myclassmethod(object):    ...:     def __init__(self, func):    ...:         self._func = func    ...:     def __get__(self, inst, cls):    ...:         return partial(self._func, cls)  in [6]: class a(object):    ...:     @myclassmethod    ...:     def foo(cls):    ...:         print('in class: {}'.format(cls))    ...:           in [7]: a.foo() in class: <class '__main__.a'>  in [8]: a().foo() in class: <class '__main__.a'>