def _add_bound_method(self, bound_method, identify_observed):
        """Add an bound method as an observer.

        Args:
            bound_method: The bound method to add as an observer.
            identify_observed: See the docstring for add_observer.

        Returns:
            True if the bound method is added, otherwise False.
        """

        inst = bound_method.__self__
        method_name = bound_method.__name__
        key = self.make_key(bound_method)
        if key not in self.observers:
            self.observers[key] = ObserverBoundMethod(
                inst, method_name, identify_observed, (key, self.observers))
            return True
        else:
            return False
Add an bound method as an observer.

        Args:
            bound_method: The bound method to add as an observer.
            identify_observed: See the docstring for add_observer.

        Returns:
            True if the bound method is added, otherwise False.