方法的描述符__get__

Question

I'm trying to understand what the __get__ descriptor is doing in code below. I have wrote all tutorial about __get__ , still can't get what's happening here.

class A:
    def __init__(self, socket, address=None):
      self.sock = socket
      self.address = address
      self.verbose = True

class B():
    def __init__(self):
      self.clients = []
      self.slaves = []
      self.pending_tasks = []
      self.running_tasks = {}
      self.finished_tasks = {}


class C(B):
    def __init__(self, *args, **kwargs):
        super(C, self).__init__(*args, **kwargs)


    def handle_new_connection(self, socket, address):
        link = A(socket, address)

    def bind(self, host, port):
        handle = self.handle_new_connection.__get__(self, C)

if __name__ == "__main__":
    m = C()
    m.bind('0.0.0.0', 6666)

What the __get__ is doing in bind method?

Answer 1

The __get__ call is redundant and useless. The method is already bound , all the __get__ call does is bind it again:

>>> m = C()
>>> m
<__main__.C object at 0x10b2cbeb8>
>>> m.handle_new_connection
<bound method C.handle_new_connection of <__main__.C object at 0x10b2cbeb8>>
>>> m.handle_new_connection.__get__(m, C)
<bound method C.handle_new_connection of <__main__.C object at 0x10b2cbeb8>>

Note how the __get__ method call on the already bound method object returned the bound method object itself; nothing changed here.

The only reason I can think of to jump through this hoop (other than not understanding that a Python method lookup already invoked the function descriptor), is to be able to call the method as a class method (by passing in an explicit first argument that is not an instance but a class):

>>> C.handle_new_connection
<function C.handle_new_connection at 0x10b5e32f0>
>>> C.handle_new_connection.__get__(C, C)
<bound method type.handle_new_connection of <class '__main__.C'>>
>>> C.bind(C, '0.0.0.0', 6666)

because in that case self.handle_new_connection resolves into the original unbound function.