# 3 - Functions

In the chapter [Variable, expressions and statements](variables-expressions-and-statements) we have seen some of the fundamental programming techniques to write simple program. This chapter introduces Python functions to perform common operations. First, we will study the **built-in** functions provided with the Python language. Secondly, we will be looking at common mathematical operations provided by the `math` module. Finally, we will learn how to create our own custom functions.

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