Output of the Python program is coming as 'None'

Question

def fact(n, summ):
    if n == 0:
        print(summ)  -- Prints 55
        return summ
    fact(n-1, summ + n)


print(fact(10, 0))  -- Output None

Yes I understand, but why does it return 'None' if I return it from inside the IF block ? — Dhruv, Jul 01 '18 at 15:35
@Dhruv Because it only returns from the block when `n == 0`, so `None` is implicitly returned if nothing else is. Think of the flow of data between recurses. Every path of execution must return something or that data is lost. — Carcigenicate, Jul 01 '18 at 16:01

blhsing · Answer 1 · 2018-07-01T15:39:26.147

You need to return fact(n-1, summ + n) as a returning value. If a function does not return a value then it defaults to returning None.

def fact(n, summ):
    if n == 0:
        return summ
    return fact(n-1, summ + n)

print(fact(10, 0))

This outputs:

On a side note, your fact function could be re-implemented without the second parameter. The following produces the same output:

def fact(n):
    if n == 0:
        return 0
    return n + fact(n-1)

print(fact(10))

1 Answers1