Contents
Introduction
This week, you are going to learn about more complex objects. These are objects capable of keeping track of more than one piece of information...
The Vending Machine Metaphor
Think about vending machines. As an idea, they are all vending machines. But in real life, they are all unique vending machines, each with different prices and food choices....

Class Functions

This week, we will be introducing another fundamental piece of complex objects: Class Functions. Class Functions, or member functions, are functions that belong to a specific object.

Definition Class Functions - A function packaged within a class. These functions allow us to use or modify the objects stored inside a complex object.

These functions reside within complex objects, just like attributes. They allow us to make changes to or take advantage of the attributes of a specific complex object.

Example: The Bot Class

Let us say that we have a Bot class, that allows us to build robots capable of buying and holding sodas. These Bot objects have 4 attributes: name, age, charge, and num_sodas. They as well have two class functions: buy_sodas and is_holding_sodas. Without getting into the specifics, let us take a look at the following piece of code:

geoff_bot = Bot("GeoffBot")
sabri_bot = Bot("SabriBot")

print(geoff_bot.charge)     # 100.0 charge
print(geoff_bot.num_sodas)  # 0 sodas

print(sabri_bot.charge)     # 100.0 charge
print(sabri_bot.num_sodas)  # 0 sodas

geoff_bot.buy_sodas(4)

print(geoff_bot.charge)     # 93.2 charge
print(geoff_bot.num_sodas)  # 4 sodas

print(sabri_bot.charge)     # 100.0 charge
print(sabri_bot.num_sodas)  # 0 sodas

Here we see that calling the function buy_sodas changes the attributes of geoff_bot, but not the attributes of sabri_bot. This is because the function uses and modifies the object to which it is attached.

Syntax of Class Functions

These functions are just like any other functions. They can take objects (parameters) and return objects. However, the only difference is that they must be attached to an object of the right class. This is because these functions often use information attached to the class of interest. We can use these functions by using the “dot” notation that we saw in the Complex Objects notes. Here we can see an example of a class function returning True or False, depending on whether or not the specific Bot object is currently holding sodas.

print(geoff_bot.is_holding_sodas()) # True
print(sabri_bot.is_holding_sodas()) # False

Class Functions are powerful and extremely common in Python. They allow programmers to create powerful classes that are both organized and easy to use. By packaging code into classes, programmers are able to share code and build versatile progams that are easy to expand and improve.