Python: writing function mult(a,b) for a*b with only add/sub/neg, recursion error for testing (-a,b)

Question

I have this so far - but if I test with (-a, b), python gives me a recursion error. Please help, not sure why this isn't working. All other tests work here.

def mult(a, b):
""" mult returns the product of two inputs
    inputs: n and m are integers
    output: result of multiplying n and m
""" 
    if b < 0:
       return -mult(a,-b)
    elif b == 0:
       return 0
    elif b == 1:
       return a
    else:
       return a + mult(a,b-1)

Thanks out there.

Please show the full traceback of the error. Also, the indentation of your shown code is wrong, so you should get a syntax error. Finally, the check for `b == 1` is extraneous and not needed: `b` will become zero in the next recursion step. — Rory Daulton, Sep 11 '16 at 22:18
This code works for me, after correcting the indentation. Please show the values for which the function fails. — David Harris, Sep 11 '16 at 23:02

score 1 · Answer 1 · edited May 23 '17 at 12:32

1

Python has a limit to the number of recursions. You may just be hitting into it. See the following answer:

What is the maximum recursion depth in Python, and how to increase it?

edited May 23 '17 at 12:32

Community

1
1

answered Sep 11 '16 at 22:25

user2539336

180
6

Yeah, typically around 1000. What were your inputs? – Rex D Sep 12 '16 at 00:21

Python: writing function mult(a,b) for a*b with only add/sub/neg, recursion error for testing (-a,b)

1 Answers1