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

11.2 Factorials

Let’s write a program to perform a famous mathematical calculation. Consider the factorial of a positive integer n, which is written n! and pronounced “n factorial.” This is the product

n · (n – 1) · (n – 2) · … · 1

with 1! equal to 1 and 0! defined to be 1. For example, 5! is the product 5 · 4 · 3 · 2 · 1, which is equal to 120.

Iterative Factorial Approach

You can calculate 5! iteratively with a for statement, as in:

In [1]: factorial = 1

In [2]: for number in range(5, 0, -1):
   ...:     factorial *= number
   ...:

In [3]: factorial
Out[3]: 120