math.py 文件源码

def string_to_natural(s, alphabet=None):
    if alphabet is None:
        assert not s.startswith('\x00')
        return int(s.encode('hex'), 16) if s else 0
    else:
        assert len(set(alphabet)) == len(alphabet)
        assert not s.startswith(alphabet[0])
        return sum(alphabet.index(char) * len(alphabet)**i for i, char in enumerate(reversed(s)))