Compute sum of single-digit numbers

sdc.py

#coding: utf-8

import sys

def count(v):
    """
    Get sum of single-digit numbers in string. Use 'x' for 10.

    >>> count("123")
    6
    >>> count("123x")
    16
    """
    sc = 0
    for d in v:
        assert d in "0123456789xX"
        sc += 10 if d in "xX" else (ord(d) - ord('0'))
    return sc

if __name__ == '__main__':
    sys.stdout.write("%d\n" % count(sys.argv[1]))

# python -m doctest -v ./sdc.py