A function in Python can call itself. That’s what recursion is. And it can be pretty useful in many scenarios.

The common way to explain recursion is by using the factorial calculation.

The factorial of a number is the number n mutiplied by n-1, multiplied by n-2… and so on, until reaching the number 1:

3! = 3 * 2 * 1 = 6
4! = 4 * 3 * 2 * 1 = 24
5! = 5 * 4 * 3 * 2 * 1 = 120


Using recursion we can write a function that calculates the factorial of any number:

def factorial(n):
if n == 1: return 1
return n * factorial(n-1)

print(factorial(3)) #   6
print(factorial(4)) #  24
print(factorial(5)) # 120


If inside the factorial() function you call factorial(n) instead of factorial(n-1), you are going to cause an infinite recursion. Python by default will halt recursions at 1000 calls, and when this limit is reached, you will get a RecursionError error.

Recursion is helpful in many places, and it helps us simplify our code when there’s no other optimal way to do it, so it’s good to know this technique.

## One more thing! ⚠️ ✋

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It's a 10-weeks long cohort online course where I will guide you to becoming a Web Developer.

It's not "just a course". It's a big event I organize once a year.

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At the end of the first 10 weeks you'll know how to create web sites and web applications and I'll unlock you the 2nd phase of the Bootcamp: you will get access to a large number of projects exclusive to the Bootcamp graduates, so you can follow my instructions to build things like private areas with authentication, clones of popular sites like Twitter YouTube Reddit, create e-commerce sites, and much much more.

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