Introduction to Classes

Learn what classes are, why they're important, and how to use them effectively.

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Lesson 1 of 2

1
Why Use Classes?
Python is an object-oriented programming language, which means it manipulates programming constructs called objects. You can think of an object as a single data structure that contains data as we…
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2
Class Syntax
A basic class consists only of the class keyword, the name of the class, and the class from which the new class inherits in parentheses. (We’ll get to inheritance soon.) For now, our classes wi…
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3
Classier Classes
We’d like our classes to do more than… well, nothing, so we’ll have to replace our pass with something else. You may have noticed in our example back in the first exercise that we started our …
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4
Let's Not Get Too Selfish
Excellent! Let’s make one more tweak to our class definition, then go ahead and instantiate (create) our first object. So far, init() only takes one parameter: self. This is a Python conve…
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5
Instantiating Your First Object
Perfect! Now we’re ready to start creating objects. We can access attributes of our objects using dot notation. Here’s how it works: class Square(object): def init(self): self.sides =…
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6
More on __init__() and self
Now that you’re starting to understand how classes and objects work, it’s worth delving a bit more into init() and self. They can be confusing! As mentioned, you can think of init() as the…
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7
Class Scope
Another important aspect of Python classes is scope. The scope of a variable is the context in which it’s visible to the program. It may surprise you to learn that not all variables are accessib…
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8
A Methodical Approach
When a class has its own functions, those functions are called methods. You’ve already seen one such method: init(). But you can also define your own methods!
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9
They're Multiplying!
A class can have any number of member variables. These are variables that are available to all members of a class. hippo = Animal(“Jake”, 12) cat = Animal(“Boots”, 3) print hippo.is_alive hipp…
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10
It's Not All Animals and Fruits
Classes like Animal and Fruit make it easy to understand the concepts of classes and instances, but you probably won’t see many zebras or lemons in real-world programs. However, classes and object…
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11
Warning: Here Be Dragons
Inheritance is a tricky concept, so let’s go through it step by step. Inheritance is the process by which one class takes on the attributes and methods of another, and it’s used to express an *i…
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12
Inheritance Syntax
In Python, inheritance works like this: class DerivedClass(BaseClass): # code goes here where DerivedClass is the new class you’re making and BaseClass is the class from which that new class i…
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13
Override!
Sometimes you’ll want one class that inherits from another to not only take on the methods and attributes of its parent, but to override one or more of them. class Employee(object): def __init…
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14
This Looks Like a Job For...
On the flip side, sometimes you’ll be working with a derived class (or subclass) and realize that you’ve overwritten a method or attribute defined in that class’ base class (also called a *parent…
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15
Class Basics
First things first: let’s create a class to work with.
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16
Class It Up
Great! Now let’s add a member variable and a method to our class.
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17
Instantiate an Object
Let’s go ahead and create an instance of our Triangle class.
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18
Inheritance
Finally, let’s create an Equilateral class that inherits from our Triangle class. (An equilateral triangle is a triangle whose angles are all 60˚, which also means that its three sides are equal in…
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