signals.py 文件源码

def _call_callback(self, callback, user_arg, user_args, emit_args):
        if user_args:
            args_to_pass = []
            for arg in user_args:
                if isinstance(arg, weakref.ReferenceType):
                    arg = arg()
                    if arg is None:
                        # If the weakref is None, the referenced object
                        # was cleaned up. We just skip the entire
                        # callback in this case. The weakref cleanup
                        # handler will have removed the callback when
                        # this happens, so no need to actually remove
                        # the callback here.
                        return False
                args_to_pass.append(arg)

            args_to_pass.extend(emit_args)
        else:
            # Optimization: Don't create a new list when there are
            # no user_args
            args_to_pass = emit_args

        # The deprecated user_arg argument was added to the end
        # instead of the beginning.
        if user_arg is not None:
            args_to_pass = itertools.chain(args_to_pass, (user_arg,))

        return bool(callback(*args_to_pass))