Recursion

Recursion refers to recursive functions; functions which call themselves. Recursion can be used in a similar manner to looping. However, in Python, recursion is generally less useful than loops.

To start, Python has a built-in recursion depth that prevents recursion from going to far— this is to prevent run-away recursion from resultin gin a crash, memory overuse, or both.

def infinite(num):
	print(num, end='\r')
	infinite(num+1)

If the function calls itself too many times, it will arbitrarily be terminated, and an exception will be thrown.

try:
	infinite(5)
except RecursionError:
	print("Maximum recursion depth exceeded.")

That being said, there are some cases where recursion makes more sense than alternative methods of performing certain tasks.

def factorial(n):
	if n > 1:
		return n * factorial(n-1)
	else:
		return 1

print(factorial(5))
120

A looping factorial function, by comparison, might look like this:

def factorial(n):
   product = 1
   for i in range(1, n+1):
      product *= i
   
   return product

print(factorial(5))
120

In practice, recursion usually turns out to be completely optional. There are almost always different, if not better ways to do things.