Make it reusable

Your own functions

Lesson 5 of 20 · 7 min · Module 2: Loops & functions

Functions turn an idea into a reusable tool. Define one with def, give it a name, and let it return a result.

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By the end, you’ll be able to…

Define a function with def
Use a parameter in a calculation
Return a result for a caller to use

The idea

The function’s body is indented. Use return to provide a value to the caller. You can pass different values into the same function.

def greet(name):
    return "Hello, " + name

print(greet("Alex"))

01Definition and execution are different

def creates a function. The function body runs later, when called. Its parameter gets the value supplied by the caller.

def square(number):
    return number * number

print(square(4))

Output

02Replace a placeholder with behavior

pass is a valid empty statement that makes the starter syntactically complete. It does not calculate or return a useful value. Replace it with the function’s real work.

Your turn

Define square(number) to return the number multiplied by itself. Print square(5).

What the checks look for

square(5) returns 25
Handles zero and negative numbers
Prints 25

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Take this with you

Functions package behavior around an explicit input and output.