How do you check whether a python method is bound or not?

Question

Given a reference to a method, is there a way to check whether the method is bound to an object or not? Can you also access the instance that it\'s bound to?

Answer 1

A solution that works for both Python 2 and 3 is tricky.

Using the package six, one solution could be:

def is_bound_method(f):
    """Whether f is a bound method"""
    try:
        return six.get_method_self(f) is not None
    except AttributeError:
        return False

In Python 2:

• A regular function won't have the im_self attribute so six.get_method_self() will raise an AttributeError and this will return False
• An unbound method will have the im_self attribute set to None so this will return False
• An bound method will have the im_self attribute set to non-None so this will return True

In Python 3:

• A regular function won't have the __self__ attribute so six.get_method_self() will raise an AttributeError and this will return False
• An unbound method is the same as a regular function so this will return False
• An bound method will have the __self__ attribute set (to non-None) so this will return True