Adding extra functionality to parent class method without changing its name [duplicate]

Question

I have two classes one parent and other child.

class Parent(object):

    def __init__(self):
        #does something

    def method_parent(self):
        print "Parent"

class Child(Parent):

    def __init__(self):
        Parent.__init__(self)

    def method_parent(self):
        print "Child"

After inheriting the parent I want to modify Parent method method_parent keeping the original functionality of that method and adding some extra lines of code to that method.

I know that I can create a new method like

def method_child(self):
    self.method_parent()
    #Add extra lines of code to perform something 

But I want to use the original name of method. I can't copy the source for that method because, the method is from a C module

what I want to achieve is something like this

def method_parent():
    #do parent_method stuff
    #do extra stuff

Is that even possible?

Answer 1

You can always call code from the parent using the super() function. It gives a reference to the parent. So, to call parent_method(), you should use super().parent_method().

Here's a code snippet (for python3) that shows how to use it.

class ParentClass: 
    def f(self): 
        print("Hi!"); 

class ChildClass(ParentClass): 
    def f(self):
        super().f(); 
        print("Hello!"); 

In python2, you need to call super with extra arguments: super(ChildClass, self). So, the snippet would become:

class ParentClass: 
    def f(self): 
        print("Hi!"); 

class ChildClass(ParentClass): 
    def f(self):
        super(ChildClass, self).f(); 
        print("Hello!"); 

If you call f() on an instance of ChildClass, it will show: "Hi! Hello!".

If you already coded in java, it's basically te same behaviour. You can call super wherever you want. In a method, in the init function, ...

There are also other ways to do that but it's less clean. For instance, you can do:

ParentClass.f(self) 

To call the f function of parent class.

Answer 2

This is what the super function does.

class Child(Parent):

    def __init__(self):
        super(Child, self).__init__()

    def method_parent(self):
        super(Child, self).method_parent()
        print "Child"

In Python 3, you can call super without the arguments, like super().method_parent()