parse 对八种输入的判决

parse 把一行输入变成整数、命令或 None（不合法）。看它对八种输入各给什么：

def parse(line):
    s = line.strip()
    if s in ("q", "r"):
        return s
    if not s.isdigit():
        return None
    n = int(s)
    if n < 1 or n > 100:
        return None
    return n

raw = ["50", " 7 ", "abc", "0", "101", "q", "", "-5"]
print(",".join(str(parse(x)) for x in raw))