Traceback (most recent call last): File "src.py", line 9, in <module> fa(x,y) File "src.py", line 5, in fa x*=fa(x,y-1) File "src.py", line 5, in fa x*=fa(x,y-1) TypeError: unsupported operand type(s) for *: 'int' and 'NoneType'