Comment calculer le nombre d'un chiffre en entier (python)

def rep_len(num, base = 10):
    if num == 0 :
        return 1
    if num < 0:
        raise ValueError( "num argument must be positive")
    ncar = 0
    while num > 0:
        num /= base;
        ncar += 1
    return ncar

for x, base in ( (0, 10), (5, 10), (10, 16), (348, 7)) :
    print("%d in base %d: %d\n" %(x, base, rep_len(x, base) ))

print(rep_len(-2))

johand@bata:~/src/CCM/PYTHON$ python rep_len.py 
0 in base 10: 1

5 in base 10: 1

10 in base 16: 1

348 in base 7: 4

Traceback (most recent call last):
  File "rep_len.py", line 15, in <module>
    print(rep_len(-2))
  File "rep_len.py", line 5, in rep_len
    raise ValueError( "num argument must be positive")
ValueError: num argument must be positive