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Learn Python: Inheritance and Polymorphism
Overriding Methods

Inheritance is a useful way of creating objects with different class variables, but is that all it’s good for? What if one of the methods needs to be implemented differently? In Python, all we have to do to override a method definition is to offer a new definition for the method in our subclass.

An overridden method is one that has a different definition from its parent class. What if User class didn’t have an is_admin flag but just checked if it had permission for something based on a permissions dictionary? It could look like this:

class User: def __init__(self, username, permissions): self.username = username self.permissions = permissions def has_permission_for(self, key): if self.permissions.get(key): return True else: return False

Above we defined a class User which takes a permissions parameter in its constructor. Let’s assume permissions is a dict. User has a method .has_permission_for() implemented, where it checks to see if a given key is in its permissions dictionary. We could then define our Admin user like this:

class Admin(User): def has_permission_for(self, key): return True

Here we define an Admin class that subclasses User. It has all methods, attributes, and functionality that User has. However, if you call has_permission_for on an instance of Admin, it won’t check its permissions dictionary. Since this User is also an Admin, we just say they have permission to see everything!

Instructions

1.

In script.py, we’ve defined two classes, Message and User. Create an Admin class that subclasses the User class.

2.

Override User‘s .edit_message() method in Admin so that an Admin can edit any messages.

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