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Functions
Functions are a significant part of Python and most other languages. They are units of code that carry out a specific set of operations. And while functions can be called many times throughout a program, there are plenty of cases where a function is called just once but conveniently groups a set of operations that you need to call within a program.
Functions are usually called with one or more arguments and usually return some value when they exit. To declare a function, start with the def keyword and end the declaration with parentheses and a colon. The actual code is indented four spaces, just as we saw for looping code. Let’s write a really simple function first that calculates the square of a number:
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