Get overridden functions of subclass

Question

Is there a way to get all overriden functions of a subclass in Python?

Example:

class A:
    def a1(self):
        pass

    def a2(self):
        pass


class B(A):
    def a2(self):
        pass

    def b1(self):
        pass

Here, I would like to get a list ["a2"] for an object of class B (or for the class object itself) since class B overrides only a single method, namely a2.

score 18 · Accepted Answer · answered Oct 24 '19 at 12:13

18

You can access the parent classes with cls.__bases__, find all attributes of the parents with dir, and access all the attributes of the class itself with vars:

def get_overridden_methods(cls):
    # collect all attributes inherited from parent classes
    parent_attrs = set()
    for base in cls.__bases__:
        parent_attrs.update(dir(base))

    # find all methods implemented in the class itself
    methods = {name for name, thing in vars(cls).items() if callable(thing)}

    # return the intersection of both
    return parent_attrs.intersection(methods)

>>> get_overridden_methods(B)
{'a2'}

answered Oct 24 '19 at 12:13

Aran-Fey

39,665
11
104
149

`vars` was the thing i was missing. big thanks for the (incredibly) fast answer! – Andreas Schörgenhumer Oct 24 '19 at 12:19
`parent_attrs` in one line if you want: `parent_attrs = {a for b in cls.__bases__ for a in dir(b)}` – wjandrea Oct 24 '19 at 21:06

score 3 · Answer 2 · answered Oct 24 '19 at 12:04

3

You can make use of the __mro__ tuple, which holds the method resolution order.

For your example:

>>> B.__mro__
( <class '__main__.B'>, <class '__main__.A'>, <class 'object'>)

So you could loop over that tuple and check if a B method is also in one of the other classes.

answered Oct 24 '19 at 12:04

Adelin

7,809
5
37
65

This will not exclude predefined method, like any **dunder** method , `__init__, __eq__, ....... etc` – Charif DZ Oct 24 '19 at 12:33

score -1 · Answer 3 · edited Oct 24 '19 at 21:09

-1

class A:

    def a1(self):
        pass

    def a2(self):
        pass


class B(A):

    def a2(self):
        super().a2()  
        pass

    def b1(self):
        pass
obj = B()

obj.a2()   # ***first give the output of parent class then child class***

edited Oct 24 '19 at 21:09

wjandrea

28,235
9
60
81

answered Oct 24 '19 at 13:30

Manish Kumar

554
4
7

2

I think you misunderstood the question. Classes `A` and `B` can't be modified. OP wants to know which of `B`'s methods override one of `A`'s methods. – wjandrea Oct 24 '19 at 21:10

Get overridden functions of subclass

3 Answers3