5. Classes

You are already familiar with defining your own functions, like this:

def f(a):
    return a

f(2)

2

But what about defining your own types? First, lets remind ourselves of some built-in types:

a = 2

type(a)

int

OK, so there is a thing called an int.

int

int

We can make a new int by calling the type name as a function:

int()

0

To build our own type, we can use the class keyword:

class MyClass:
    pass

MyClass

__main__.MyClass

instance = MyClass()

type(instance)

__main__.MyClass

5.1. What is this good for?

The essence of object-oriented programming is allowing for data and algorithms to be combined in one place. Functions allow us to re-use algorithms, but classes allow us to combine them with local data:

class MyClass2:
    def __init__(self, name):
        print("I'm in __init__!")
        self.name = name

    def say_my_name(self):
        print(self.name)

s = MyClass2('Carl')

I'm in __init__!

s.say_my_name()

Carl

5.2. Objects must be “like” things

class Person:
    def __init__(self, name):
        self.name = name

    def display_name(self):
        print(self.name)

carl = Person("Carl Sandrock")

carl.display_name()

Carl Sandrock