如何使用 strptime 解析 str(my_datetime)?

2022-01-16 00:00:00 python datetime timezone strptime

问题描述

这是 默认字符串表示日期时间:

>>> from datetime import datetime, timezone
>>> dt = datetime(2017, 1, 1, tzinfo=timezone.utc)
>>> print(dt)
2017-01-01 00:00:00+00:00

datetime.strptime 解析的正确格式字符串是什么?也就是说,用什么格式代替???"?始终具有以下不变量:

What is the correct format string to parse that with datetime.strptime? That is, what format goes in place of the "???" to consistently have the following invariant:

>>> dt == datetime.strptime(str(dt), "???")
True


解决方案

注意 str(d) 被记录为等同于 d.isoformat(' ').这以 %Y-%m-%d %H:%M:%S (2017-01-01 00:00:00) 开头,然后:

Note that str(d) is documented as being equivalent to d.isoformat(' '). This starts with %Y-%m-%d %H:%M:%S (2017-01-01 00:00:00), but then:

  • 要么没有,要么没有 .%f,这取决于微秒部分是否为非零.
  • 根据实例是否支持时区,要么没有任何内容,要么没有类似 +HH:MM 的偏移量.
  • Either has nothing or .%f, depending whether the microseconds part is nonzero.
  • Either has nothing or an offset like +HH:MM, depending whether the instance is timezone-aware.

datetime.strptime 不支持可选部分,因此没有一个 format 参数可以匹配所有可能的输出.

datetime.strptime doesn't have support for optional parts, therefore there isn't a single format parameter that can match all of the possible outputs.

在 Python 3.7+ 中,您可以使用 datetime.fromisoformat 解析 datetime.isoformat 输出.由 Paul Ganssle 在 issue15873 中贡献.

In Python 3.7+, you can use datetime.fromisoformat to parse datetime.isoformat output. Contributed by Paul Ganssle in issue15873.

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