是否可以从父类调用子类的函数？

Question

class A(object):
    def xx():
        # do something

    def yy():
        # do something

class B(A):
    def func():
        # do something

# How to make it possible?
a = A()
a.func()

Now I want to add func() to class A, however I CANNOT change class A, so I created a subclass of A and add func() to the subclass. How can I call func() from A instance?

I tried to initiate with class B, however, there are many instances, so I need to change many many locations. Is there a better way to do it? Ideally with class A.

# This works, however, I need to change A() to B() everywhere.
# Are there easy ways to do it without changing A() to B()?
a = B()
a.func()

Answer 1

You could use setattr() ( doc ):

class A:
    def xx(self):
        print('xx')

    def yy(self):
        print('yy')

class B(A):
    def func(self):
        print('func')

setattr(A, 'func', B.func) # or setattr(A, B.func.__name__, B.func)

a = A()
a.func()

Prints:

func

Answer 2

You can't do such thing because class B inherits from Class A not the reverse, so you can use B.xx() but you can't use A.func().

For more information about inheritance in Python, look here

As Andrej said, you can use setattr() method to define new attribute for class A. Look here for more information about setattr() method.