Python datetime：tz inside 方法和 .replace(tzinfo=) 之间的区别答案

【问题标题】：Python datetime: difference between tz inside method and .replace(tzinfo=)Python datetime：tz inside 方法和 .replace(tzinfo=) 之间的区别
【发布时间】：2019-01-15 09:26:51
【问题描述】：

我最近修复了一个错误，但仍然不知道为什么会发生。我有以下将时间戳（纪元）转换为 Django 模型中的日期时间字段：

our_timezone = pytz.timezone("Asia/Jerusalem")
# e13 is used for true division
final_dict["published_date"] = datetime.datetime.fromtimestamp(
            float(article_as_dict["publish_date"]) / 1e3).replace(tzinfo=our_timezone)

上面的返回了一个日期时间对象，它总是比真正的纪元时间（在我们的时区）晚 39 分钟。

我设法通过删除replace 来修复它，而是将时区放在fromtimestamp 方法中：

final_dict["published_date"] = datetime.datetime.fromtimestamp(
            float(article_as_dict["publish_date"]) / 1e3, tz=our_timezone)

那么在fromtimestamp 方法中指定tz=our_timezone 与在创建对象后执行.replace(tzinfo=our_timezone) 有什么区别？为什么.replace 会返回错误的时间？

【问题讨论】：

标签： python datetime

【解决方案1】：

>>> datetime.fromtimestamp(1000000000).replace(tzinfo=our_timezone)
datetime.datetime(2001, 9, 9, 3, 46, 40, tzinfo=<DstTzInfo 'Asia/Jerusalem' LMT+2:21:00 STD>)
>>> datetime.fromtimestamp(1000000000, tz=our_timezone)
datetime.datetime(2001, 9, 9, 4, 46, 40, tzinfo=<DstTzInfo 'Asia/Jerusalem' IDT+3:00:00 DST>)

注意第一种情况下的奇数时区偏移量。

时区是多个偏移量的集合。时区偏移随时间而变化。它不仅会根据夏季和冬季时间在一年内发生变化，而且在修改和更新时区数据时也会发生历史变化。您可以检查时区对象以获取一些有趣的历史数据，这些数据可以追溯到几十年前：

>>> our_timezone._utc_transition_times
[datetime.datetime(1, 1, 1, 0, 0), datetime.datetime(1901, 12, 13, 20, 45, 52), datetime.datetime(1917, 12, 31, 21, 39, 20), datetime.datetime(1940, 5, 31, 22, 0), datetime.datetime(1942, 10, 31, 21, 0), datetime.datetime(1943, 4, 1, 0, 0), datetime.datetime(1943, 10, 31, 21, 0), datetime.datetime(1944, 3, 31, 22, 0), datetime.datetime(1944, 10, 31, 21, 0), datetime.datetime(1945, 4, 15, 22, 0), datetime.datetime(1945, 10, 31, 23, 0), datetime.datetime(1946, 4, 16, 0, 0), datetime.datetime(1946, 10, 31, 21, 0), datetime.datetime(1948, 5, 22, 22, 0), datetime.datetime(1948, 8, 31, 20, 0), datetime.datetime(1948, 10, 31, 23, 0), datetime.datetime(1949, 4, 30, 22, 0), datetime.datetime(1949, 10, 31, 23, 0), datetime.datetime(1950, 4, 15, 22, 0), datetime.datetime(1950, 9, 15, 0, 0), datetime.datetime(1951, 3, 31, 22, 0), datetime.datetime(1951, 11, 11, 0, 0), datetime.datetime(1952, 4, 20, 0, 0), datetime.datetime(1952, 10, 19, 0, 0), datetime.datetime(1953, 4, 12, 0, 0), datetime.datetime(1953, 9, 13, 0, 0), datetime.datetime(1954, 6, 12, 22, 0), datetime.datetime(1954, 9, 11, 21, 0), datetime.datetime(1955, 6, 11, 0, 0), datetime.datetime(1955, 9, 10, 21, 0), datetime.datetime(1956, 6, 2, 22, 0), datetime.datetime(1956, 9, 30, 0, 0), datetime.datetime(1957, 4, 29, 0, 0), datetime.datetime(1957, 9, 21, 21, 0), datetime.datetime(1974, 7, 6, 22, 0), datetime.datetime(1974, 10, 12, 21, 0), datetime.datetime(1975, 4, 19, 22, 0), datetime.datetime(1975, 8, 30, 21, 0), datetime.datetime(1985, 4, 13, 22, 0), datetime.datetime(1985, 9, 14, 21, 0), datetime.datetime(1986, 5, 17, 22, 0), datetime.datetime(1986, 9, 6, 21, 0), datetime.datetime(1987, 4, 14, 22, 0), datetime.datetime(1987, 9, 12, 21, 0), datetime.datetime(1988, 4, 9, 22, 0), datetime.datetime(1988, 9, 3, 21, 0), datetime.datetime(1989, 4, 29, 22, 0), datetime.datetime(1989, 9, 2, 21, 0), datetime.datetime(1990, 3, 24, 22, 0), datetime.datetime(1990, 8, 25, 21, 0), datetime.datetime(1991, 3, 23, 22, 0), datetime.datetime(1991, 8, 31, 21, 0), datetime.datetime(1992, 3, 28, 22, 0), datetime.datetime(1992, 9, 5, 21, 0), datetime.datetime(1993, 4, 1, 22, 0), datetime.datetime(1993, 9, 4, 21, 0), datetime.datetime(1994, 3, 31, 22, 0), datetime.datetime(1994, 8, 27, 21, 0), datetime.datetime(1995, 3, 30, 22, 0), datetime.datetime(1995, 9, 2, 21, 0), datetime.datetime(1996, 3, 14, 22, 0), datetime.datetime(1996, 9, 15, 21, 0), datetime.datetime(1997, 3, 20, 22, 0), datetime.datetime(1997, 9, 13, 21, 0), datetime.datetime(1998, 3, 19, 22, 0), datetime.datetime(1998, 9, 5, 21, 0), datetime.datetime(1999, 4, 2, 0, 0), datetime.datetime(1999, 9, 2, 23, 0), datetime.datetime(2000, 4, 14, 0, 0), datetime.datetime(2000, 10, 5, 22, 0), datetime.datetime(2001, 4, 8, 23, 0), datetime.datetime(2001, 9, 23, 22, 0), datetime.datetime(2002, 3, 28, 23, 0), datetime.datetime(2002, 10, 6, 22, 0), datetime.datetime(2003, 3, 27, 23, 0), datetime.datetime(2003, 10, 2, 22, 0), datetime.datetime(2004, 4, 6, 23, 0), datetime.datetime(2004, 9, 21, 22, 0), datetime.datetime(2005, 4, 1, 0, 0), datetime.datetime(2005, 10, 8, 23, 0), datetime.datetime(2006, 3, 31, 0, 0), datetime.datetime(2006, 9, 30, 23, 0), datetime.datetime(2007, 3, 30, 0, 0), datetime.datetime(2007, 9, 15, 23, 0), datetime.datetime(2008, 3, 28, 0, 0), datetime.datetime(2008, 10, 4, 23, 0), datetime.datetime(2009, 3, 27, 0, 0), datetime.datetime(2009, 9, 26, 23, 0), datetime.datetime(2010, 3, 26, 0, 0), datetime.datetime(2010, 9, 11, 23, 0), datetime.datetime(2011, 4, 1, 0, 0), datetime.datetime(2011, 10, 1, 23, 0), datetime.datetime(2012, 3, 30, 0, 0), datetime.datetime(2012, 9, 22, 23, 0), datetime.datetime(2013, 3, 29, 0, 0), datetime.datetime(2013, 10, 26, 23, 0), datetime.datetime(2014, 3, 28, 0, 0), datetime.datetime(2014, 10, 25, 23, 0), datetime.datetime(2015, 3, 27, 0, 0), datetime.datetime(2015, 10, 24, 23, 0), datetime.datetime(2016, 3, 25, 0, 0), datetime.datetime(2016, 10, 29, 23, 0), datetime.datetime(2017, 3, 24, 0, 0), datetime.datetime(2017, 10, 28, 23, 0), datetime.datetime(2018, 3, 23, 0, 0), datetime.datetime(2018, 10, 27, 23, 0), datetime.datetime(2019, 3, 29, 0, 0), datetime.datetime(2019, 10, 26, 23, 0), datetime.datetime(2020, 3, 27, 0, 0), datetime.datetime(2020, 10, 24, 23, 0), datetime.datetime(2021, 3, 26, 0, 0), datetime.datetime(2021, 10, 30, 23, 0), datetime.datetime(2022, 3, 25, 0, 0), datetime.datetime(2022, 10, 29, 23, 0), datetime.datetime(2023, 3, 24, 0, 0), datetime.datetime(2023, 10, 28, 23, 0), datetime.datetime(2024, 3, 29, 0, 0), datetime.datetime(2024, 10, 26, 23, 0), datetime.datetime(2025, 3, 28, 0, 0), datetime.datetime(2025, 10, 25, 23, 0), datetime.datetime(2026, 3, 27, 0, 0), datetime.datetime(2026, 10, 24, 23, 0), datetime.datetime(2027, 3, 26, 0, 0), datetime.datetime(2027, 10, 30, 23, 0), datetime.datetime(2028, 3, 24, 0, 0), datetime.datetime(2028, 10, 28, 23, 0), datetime.datetime(2029, 3, 23, 0, 0), datetime.datetime(2029, 10, 27, 23, 0), datetime.datetime(2030, 3, 29, 0, 0), datetime.datetime(2030, 10, 26, 23, 0), datetime.datetime(2031, 3, 28, 0, 0), datetime.datetime(2031, 10, 25, 23, 0), datetime.datetime(2032, 3, 26, 0, 0), datetime.datetime(2032, 10, 30, 23, 0), datetime.datetime(2033, 3, 25, 0, 0), datetime.datetime(2033, 10, 29, 23, 0), datetime.datetime(2034, 3, 24, 0, 0), datetime.datetime(2034, 10, 28, 23, 0), datetime.datetime(2035, 3, 23, 0, 0), datetime.datetime(2035, 10, 27, 23, 0), datetime.datetime(2036, 3, 28, 0, 0), datetime.datetime(2036, 10, 25, 23, 0), datetime.datetime(2037, 3, 27, 0, 0), datetime.datetime(2037, 10, 24, 23, 0)]

使用datetime.fromtimestamp(1000000000)，您可以创建一个简单的时间戳，一个没有时区信息的时间戳。然后，您只需使用replace 将时区对象附加到它。这只会导致 Python 使用该时区对象中的许多偏移对象中的第一个，从而导致一百年前的奇怪偏移。

但是，将时区对象作为“上下文信息”直接提供给fromtimestamp，该方法可以选择适用于时间戳的正确偏移量并正确生成一致的时间戳对象。

您也可以在事后使用astimezone：

>>> datetime.fromtimestamp(1000000000).astimezone(our_timezone)
datetime.datetime(2001, 9, 9, 4, 46, 40, tzinfo=<DstTzInfo 'Asia/Jerusalem' IDT+3:00:00 DST>)

此方法还可以智能地选择适用的偏移量。

简而言之：replace == 愚蠢，只需覆盖原始数据，fromtimestamp，astimezone == 聪明，知道如何处理时区。

【讨论】：

多么精彩的回答。谢谢！