Question

I’m getting this error:

TypeError: unsupported operand type(s) for +: ‘int’ and ‘NoneType’

For this code:

def a(n):
    if n < 0:
        return 0
    if n == 1:
        return 1
    if n > 1:
        return a(n-1) + a(n-2) + a(n-3)

How should I call multiple recursions?

Answer 1

You are missing the condition: – 1 > n >= 0. And thus, you are not returning any value in case your n >= 0 and n < 1.

May be your first condition is supposed to be: –

if n < 1:
    return 0