Functions

A function is a reusable block of code that performs a specific task. You write it once, give it a name, and run it again anytime just by calling that name.

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

greet("Ada")   # "Hello, Ada"

A function can accept parameters (values passed in, like name above) and can return a result back to whatever called it. This reuse — write once, call many times — is one of the most important ideas in programming; later on it gets a formal name, encapsulation, but the plain idea is simply: don't repeat yourself.