Recently I came upon some code on a Python tutorial for recursion, it is a basic factorial recursion:
def factorial(n):
print("factorial has been called with n = " + str(n))
if n == 1:
return 1
else:
res = n * factorial(n-1)
print("intermediate result for ", n, " * factorial(" ,n-1, "): ",res)
return res
print(factorial(5))
This is the console output:
factorial has been called with n = 5
factorial has been called with n = 4
factorial has been called with n = 3
factorial has been called with n = 2
factorial has been called with n = 1
intermediate result for 2 * factorial( 1 ): 2
intermediate result for 3 * factorial( 2 ): 6
intermediate result for 4 * factorial( 3 ): 24
intermediate result for 5 * factorial( 4 ): 120
120
After doing some research, I feel like I have an understanding of why this is the output but I wanted to make sure. From my understanding:
it repeats the else statement 4 times and puts the n value and res value into a call stack. When res calls factorial(1), it goes to the base case and stops the recursion so we can retrieve the stack data. It pops n =1 and doesn't print any output, but then pops 2,3,4,5 and retrieves their res values that were calculated during recursion. Finally once res is returned enough, we are left with 5*24(n*res) on the top of the stack and Python knows that's the value to return for the print(factorial(5)).
Is this all correct information, am I missing something? Please let me know if any of this is incorrect or point me in a direction of some resources that can clarify this. Thank you!
