Recursion: look like same function but print out different flow of execution

Question

I tried to print out flow of execution of factorial recursion function.

def factorial(n):
    space=' '*(4*n)
    print(space,'factorial ',n)
    if n==0:
        print(space,'returning 1')
        return 1
    else:
        recurse=factorial(n-1)
        result=n*recurse
        print(space,'returning ', result)
        return n*recurse

With factorial(2) result will be correct:

        factorial 2
    factorial 1
factorial 0
returning 1
    returning 1
        returning 2
2

But when I don't use variable recurse=factorial(n-1):

def factorial(n):
    space=' '*(4*n)
    print(space,'factorial ',n)
    if n==0:
        print(space,'returning 1')
        return 1
    else:
        result=n*factorial(n-1)
        print(space,'returning ', result)
        return n*factorial(n-1)

then with factorial(2) it printed out different flow:

             factorial  2
     factorial  1
 factorial  0
 returning 1
     returning  1
 factorial  0
 returning 1
         returning  2
     factorial  1
 factorial  0
 returning 1
     returning  1
 factorial  0
 returning 1
2

My question is: why was there different flow of executions [with and without variable recurse=factorial(n-1)]?

Answer 1

This is due to below extra function call in your code

def factorial(n):
    space=' '*(4*n)
    print(space,'factorial ',n)
    if n==0:
        print(space,'returning 1')
        return 1
    else:
        result=n*factorial(n-1)
        print(space,'returning ', result)
        return n*factorial(n-1)   # factorial(n-1) is called second time so that this function is executed once again

You could do as below for similar execution

def factorial(n):
    space=' '*(4*n)
    print(space,'factorial ',n)
    if n==0:
        print(space,'returning 1')
        return 1
    else:
        result=n*factorial(n-1)
        print(space,'returning ', result)
        return result