代码实现

import re
def test_1():
    email_address = input("请输入一个邮箱地址：")
    ret = re.match(r"^[a-zA-Z0-9_]{4,20}@(163|126|gmail)\.com", email_address)
    if ret:
        print(ret.group())
    else:
        print("不符合要求")

if __name__ == '__main__':
    test_1()