方法一：

    import time
    from datetime import date

    # 时间转换成时间戳
    d = date(2022, 3, 18)
    timeArray = time.strptime(str(d), "%Y-%m-%d")
    print(timeArray)
    print(timeArray.tm_year)
    ret = int(time.mktime(timeArray))
    print(ret)

    # 时间戳转换成时间
    ret2 = time.localtime(ret)
    print(ret2)
    ret3 = time.strftime("%Y-%m-%d", ret2)
    print(ret3, type(ret3))

方法二：

 import time
 from datetime import date
 if user.birthday:
     # 日期格式转换成时间戳 user.birthday: date类型
     u_time = int(time.mktime(user.birthday.timetuple()))
     print(u_time)
     # 时间戳转换成日期
     d_time = date.fromtimestamp(u_time)
     print(d_time)