Question

I realize that this may sound like a silly question, but the last time I programmed it was in assembler so my thinking may be off:

A recursive function as so:

def fac(n):
    if n == 0:
        return 1
    else:
        return n * fac(n - 1)

Why is it that when the function reaches n == 0 that it does not return 1 but rather the answer which is the factorial. I am thinking something like in assembler it would be when n == 0:

mov eax, 1
ret

Why does the code above work, I suppose python returns the last value on the stack before that condition ?

Answer 1

Think about like this, for fac(5) for example:

return 5 * fac(4)
           return 4 * fac(3)
                      return 3 * fac(2)
                                 return 2 * fac(1)
                                            return 1 * fac(0)
                                                       1

So 1 will be the first returned value but it will be returned to fac(1) and fac(1) will be returned to fac(2) and so on.