Who doesn’t love object-oriented programming? Well, I’m ambivalent. However, as I learn more, I become more comfortable and more likely to use it. Hopefully, I become more likely to use it well. Here’s another thing I need to learn with respect to Python classes: how to inherit them.

Python Class Inheritance

A basic Python class looks like this:

class Person:
    def __init__(self,name):
        self.name = str(name)
        
    def greet(self):
        print "Hi, my name is " + self.name

See? Easy. Now, let’s extend this class:

class Rapper(Person):
    def __init__(self,name,alterEgo):
        self.name = str(name)
        self.alterEgo = str(alterEgo)
        
    def greet(self):
        print "Hi, my name is " + self.alterEgo

So, in summary, a Person has a name, but a Rapper is a Person with an alterEgo. A Person will greet someone by saying their name, but a Rapper will greet someone with their alterEgo.

Example:

marshall = Person("Marshall Mathers")
slimShady = Rapper("Marshall Mathers","chicka chicka Slim Shady")

marshall.greet()
slimShady.greet()

This produces the output:

Hi, my name is Marshall Mathers
Hi, my name is chicka chicka Slim Shady.

In this simple example, you can see how an inherited class (Rapper) overrides the built-in methods (init and greet) provided in the base class (Person).

Calling Base Class Methods in Inherited Classes

If you’re a programmer, you may be crying foul at this simple example because the Rapper class inheriting from the Person class is essentially useless: the Rapper class completely overrides everything within the Person class. Why bother inheriting?

It’s true: in the above example the inheritance does nothing. We can fix this though: there’s one piece of functionality that’s common between the two: setting name to the passed value. So, instead of completely reproducing this functionality in the inherited class, we can reuse the base class’s constructor so that the inheritance isn’t a complete waste of time. You do that like this (in Python 2.7):

class Person:
    def __init__(self,name):
        self.name = str(name)
        
    def greet(self):
        print "Hi, my name is " + self.name
  
class Rapper(Person):
    def __init__(self,name,alterEgo):
        Person.__init__(self,name)
        self.alterEgo = str(alterEgo)
        
    def greet(self):
        print "Hi, my name is " + self.alterEgo

The addition here is the Person line in the Rapper initialization function. That line calls the initialization function for the base class of Rapper (Person). This will set the name attribute to the passed value of name, essentially reusing the code from the Person initialization function so it doesn’t have to be completely reproduced in the Rapper class. You can reuse this approach for any built-in function in the base class, but mostly I use it for initialization functions.

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