奇怪的 Python 日期比较行为

Question

我遇到了奇怪的 Python 日期时间比较问题。我得到两个字符串格式的日期时间（来自 REST 调用，JSON）开始日期时间和结束日期时间。我必须比较当前日期时间，如果它落在这个范围内（开始日期时间和结束日期时间）采取一些行动。已知这些日期的时区是US/Eastern（美国北卡罗来纳州）。这是代码，

from pytz import timezone
from datetime import datetime

def main():

    # All the dates are in US/Eastern time zone. Time zone for USA, North Carolina
    # These dates are received from REST call in JSON
    # I need to compare the current date time, if that falls within this range take some action

    start_date_str = "7/17/2018 11:30:00 AM"
    end_date_str = "7/17/2018 2:30:00 PM"

    # To simulate current date time within the range, I will update the current date time value.
    current_est_time = datetime.now(tz=timezone('US/Eastern'))
    current_est_time = current_est_time.replace(year=2018, month=7, day=17, hour=12, minute=26)
    print current_est_time

    start_date = datetime.strptime(start_date_str,"%m/%d/%Y %I:%M:%S %p").replace(tzinfo=timezone('US/Eastern'))
    end_date = datetime.strptime(end_date_str, "%m/%d/%Y %I:%M:%S %p").replace(tzinfo=timezone('US/Eastern'))

    print start_date <= current_est_time <= end_date


if __name__ == '__main__':
    main()

如果分钟值是26，比较打印True，如果是25，打印False。

以上代码示例的输出为

2018-07-17 12:26:06.646643-04:00
 True

如果将 current_est_time 变量的分钟值更改为 25，则输出为
2018-07-17 12:25:16.582573-04:00
False

有人可以帮我吗，我哪里出错了？

Answer 1

错误是由不同的偏移 datetime.now() 调用引起的，returns：

2018-07-17 12:26:06.646643-04:00

但是您的日期比较没有类似的结构，它们在比较之前将如下所示：

2018-07-17 14:30:00-04:56

两个值的偏移量不同，当前为 4:00，开始和结束日期为 4:56

以下代码将修复它：

from pytz import timezone
from datetime import datetime

def main():

    # All the dates are in US/Eastern time zone. Time zone for USA, North Carolina
    # These dates are received from REST call in JSON
    # I need to compare the current date time, if that falls within this range take some action

    start_date_str = "7/17/2018 11:30:00 AM"
    end_date_str = "7/17/2018 2:30:00 PM"

    # To simulate current date time within the range, I will update the current date time value.
    current_est_time = datetime.now(tz=timezone('US/Eastern'))
    current_est_time = current_est_time.replace(year=2018, month=7, day=17, hour=12, minute=24).replace(tzinfo=timezone("US/Eastern"))
    print (current_est_time)

    start_date = datetime.strptime(start_date_str,"%m/%d/%Y %I:%M:%S %p").replace(tzinfo=timezone('US/Eastern'))
    end_date = datetime.strptime(end_date_str, "%m/%d/%Y %I:%M:%S %p").replace(tzinfo=timezone('US/Eastern'))
    print(start_date)
    print(current_est_time)
    print(end_date)
    print (start_date <= current_est_time <= end_date)


if __name__ == '__main__':
    main()

P.S。它是用 python3 编写的，但应该可以正常工作

Answer 2

进一步调试此问题后，.replace 方法如何处理 datetime 对象的时区信息似乎存在问题。如果我们使用 .replace 方法添加时区，start_date 中的 tzinfo 对象有 _tzname = "LMT" 和 current_est_time 中的 tzinfo 对象有 _tzname = "EDT"。这就是为什么比较结果不一致的原因。
通过参考 Why doesn't pytz localize() produce a datetime object with tzinfo matching the tz object that localized it?
，看起来 "EDT" 是正确的值。所以在我看来，这是实现它的正确方法，

from datetime import datetime
import pytz

def main():
    process_date_time(25)
    process_date_time(26)

def process_date_time(min):
    # All the dates are in US/Eastern time zone. Time zone for USA, North Carolina
    # These dates are received from REST call in JSON
    # I need to compare the current date time, if that falls within this range take some action
    tz = pytz.timezone('US/Eastern')
    start_date_str = "7/17/2018 11:30:00 AM"
    end_date_str = "7/17/2018 2:30:00 PM"

    # To simulate current date time within the range, I will update the current date time value.
    dt = datetime.now()
    current_est_time = tz.localize(dt)
    current_est_time = current_est_time.replace(year=2018, month=7, day=17, hour=12, minute=min)
    print current_est_time

    start_date_1 = datetime.strptime(start_date_str, "%m/%d/%Y %I:%M:%S %p")
    end_date_1 = datetime.strptime(end_date_str, "%m/%d/%Y %I:%M:%S %p")

    start_date = tz.localize(start_date_1)
    end_date = tz.localize(end_date_1)

    print start_date <= current_est_time <= end_date


if __name__ == '__main__':
    main()

奇怪的 Python 日期比较行为

Weird Python Date Comparison Behaviour

python

python-2.x

pytz

python-2.7

python-datetime