Python Tip - Classes

Hey. So, I thought I would write up a little something on classes in Python.
Classes are particularly useful because they represent objects in code. If you're familiar with object  oriented programming, then you already know the concept behind classes and objects in Python, but if not, it's fairly simple to learn. Let's take a look at an example.

Say you have a bicycle. Your bicycle is an object, right? What kind of object is it? Well, it's a kind of bicycle. Your bike, and all of the other bikes of the same model, were made from a prototype - a 'mold'. So, if we were to translate that to code, the prototype, or mold, would be the class, and the bike would be the object. Objects are derived from classes.

1. class Bike():
2.    
3.     __init__(self): # Lay down some initial bike stats
4.        
5.         self.color = 'White'
6.         self.wheels = 2
7.         self.motor = False
8. yourbike = Bike() # Create a new Bike object

In the example above, we define a Bike class, define its color, number of wheels, and whether or not it has a motor, and then create a new object from the class.

In line 1, we start with the class keyword - this tells Python that we're starting a new class. Notice that we put a parentheses after the class name, and then put a colon at the end. Those parentheses serve a special purpose that we'll cover later.

In line 3, we define a function called __init__(). Note that this function is named "__init__" because Python specially reserves that function in a class for initialization. Basically, if we create an object from a class, Python will call the __init__() function if it exists. Notice that there's also the self argument.

The self argument is special in classes because of two reasons.

1. The self argument is the first argument of any function created in a class.
2. The self argument refers to the object, and so can be used to store and access variables.

In the above example, we use the self variable to store information in the class object - we set the color to "White", the number of wheels to 2, and whether the bike has a motor to False. If you recall, Python is a very dynamic language - we don't have to type anything special to initialize variables. If they don't exist, they're created when we try to set them.

Finally, in line 9, we create an object from the Bike class named yourbike. We set a variable to the class name, plus parentheses - this tells Python to create an object based from the class. This represents the bike that you own earlier in the example, and with this, we created an object from the prototype (class) of the bike. We can now alter the bike object and change its attributes:

1. class Bike():
2.    
3.     __init__(self): # Lay down some initial bike stats
4.        
5.         self.color = 'White'
6.         self.wheels = 2
7.         self.motor = False
9. yourbike = Bike() # Create a new Bike object
11. yourbike.color = 'Flame Red'
12. yourbike.wheels = 4
13. yourbike.motor = True

Now, notice that by accessing yourbike, we can change its attributes that were set earlier in the class. However, if we were to create a whole new bike object from the bike class, it would still be a white bike with two wheels and no motor because yourbike is based off of the bike class, but is not a pointer to the class - it's its own object.

Why use classes? Well, it's slightly more comfortable (to me) than using dictionaries, and since you can provide initial variables as well as change variable values later, you can use these to organize things that share attributes. For example, if you have ranged weapons in a game that all have ammo, range, and projectile speed, you might use a class to represent this data.

Well, that's it for this tip. I suppose I should make more of these to further explain how classes work. Anyway, have fun messing around with classes!