8.2. Why Functions?

Functions are an essential part of most programming languages. Functions are reusable pieces of code that can be called using a function’s name. Functions can be called anywhere in a Python program, including calling functions within other functions.

Functions provide a couple of benefits:

  • Functions allow the same piece of code to run multiple times

  • Functions break long programs up into smaller components

  • Functions can be shared and used by other programmers

Every function has a function name. The function name is used when the function is called in a program. Calling a function means running a function.

Functions can receive input from the program. The input provided to a function is called input arguments or just arguments. Arguments are the code passed to a function as input.

Functions can produce output. We say a function returns output to the program. The output of a function can be assigned to a variable for use in a program.

Below is an example calling Python’s pow() a function:

out = pow(3,2)

In the function call above, the function name is pow. pow is the power function. The pow function raises a number to a power. The input arguments are the numbers 3 and 2. The function output is assigned to the variable out. In this example, the function returns the value 9 (3 raised to the 2 power, \(3^2 = 9\)).