Cookbooks
Python
Chapter 5. Good Coding Practices
Organizing code into functions

Python:
Organizing code into functions

How to:

Let’s say you’re writing a script to calculate the square and cube of a number. Without functions, it’s a mess of repetition:

num = 4
square = num * num
cube = num * num * num
print(f"Square: {square}, Cube: {cube}")

num = 5
square = num * num
cube = num * num * num
print(f"Square: {square}, Cube: {cube}")

Output:

Square: 16, Cube: 64
Square: 25, Cube: 125

With functions, it’s neater:

def square(n):
    return n * n

def cube(n):
    return n ** 3

num = 4
print(f"Square: {square(num)}, Cube: {cube(num)}")

num = 5
print(f"Square: {square(num)}, Cube: {cube(num)}")

Output:

Square: 16, Cube: 64
Square: 25, Cube: 125

Deep Dive

Back in the day, when programs were simple, you could get away with just writing a list of instructions. But as the software got more complex, developers realized they were rewriting the same code over and over. Hello, functions—reusable blocks of code that perform a single action.

Alternatives to functions include classes (bundling functions with data they operate on) and inline code (intelligence right where you need it, but risky for complex tasks). Implementation-wise, the trick is not just to create functions but to make them do one thing well—think single responsibility principle. Functions should also ideally be stateless, meaning no surprises with data coming in or going out.

See Also

LoggingRefactoring