Intro to Python for Computer Science and Data Science: Learning to Program with AI, Big Data and The Cloud

4.2 Defining Functions

You’ve called many built-in functions (int, float, print, input, type, sum, len, min and max) and a few functions from the statistics module (mean, median and mode). Each performed a single, well-defined task. You’ll often define and call custom functions. The following session defines a square function that calculates the square of its argument. Then it calls the function twice—once to square the int value 7 (producing the int value 49) and once to square the float value 2.5 (producing the float value 6.25):

In [1]: def square(number):
   ...:     """Calculate the square of number."""
   ...:     return number ** 2
   ...:

In [2]: square(7)
Out[2]: 49

In [3]: square(2.5)
Out[3]: 6.25

The statements defining the function in the first ...