Can someone explain how the source code of staticmethod works in python

Question

First of all, I understand how, in general, a decorator work. And I know @staticmethod strips off the instance argument in the signature, making

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Answer 1

A staticmethod object is a descriptor. The magic you are missing is that Python calls the __get__ method when accessing the object as an attribute on a class or instance.

So accessing the object as C.foo results in Python translating that to C.__dict__['foo'].__get__(None, C), while instance_of_C.foo becomes type(instace_of_C).__dict__['foo'].__get__(instance_of_C, type(instance_of_C)).

The staticmethod object is defined in C code, but an equivalent in Python would be:

class staticmethod(object):
    def __init__(self, callable):
        self.f = callable
    def __get__(self, obj, type=None):
        return self.f
    @property
    def __func__(self):
        return self.f

where self.f is the original wrapped function.

All this is needed because functions are themselves descriptors too; it is the descriptor protocol that gives you method objects (see python bound and unbound method object for more details). Since they too have a __get__ method, without a staticmethod object wrapping the function, a functionobj.__get__ call produces a method object instead, passing in a self argument.

There is also a classmethod, which uses the second argument to descriptor.__get__ to bind a function to the class, and then there are property objects, which translate binding into a function call directly. See How does the @property decorator work?.