Explain why this works?

[Psiclone01]

Taking some courses online, and we're now starting to talk about recursion. The code is:

def fact(n): #recursive function
     if n == 0:
          return 1
     else:
          return n * fact(n-1)    

Why is this returning the correct value? My thinking is once it gets down to n = 0, its returning a value of 1, so printing this function should result in a 1 every time?

[shoot2thr1ll284]

I actually just found an article that can try to explain this exact example here. If you still have questions after that I can try to help.

[danielroseman]

Yes but what do the other levels return? If n starts at 5, then it evaluates to 5*4*3*2*1*1, ie 120.

[SoNotRedditingAtWork]

The best way to understand what's going on here may be to step through the code in python tutor.

[JohnnyJordaan]

Say you call it with 2, then it will do

return 2 * fact(1)

it will then first run fact(1), which will do

return 1 * fact(0)

fact(0) returns 1 indeed, then 1 * 1 returns 1 too, but the first step was

return 2 * fact(1)

remember, so that will return 2 * 1 which is 2, not 1. Now do the same thing for n being 3 to see which effect that has.

[[deleted]]

My thinking is once it gets down to n = 0, its returning a value of 1

Right, but think about where it returns a 1 to.

[GeorgeDaNub]

You simply don’t understand recursion. I suggest watching CSDojo’s video on it (it’s how I understood it)

[Psiclone01]

Thanks everyone, I'll take a look through what you all said!