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Support %:z in datetime.datetime.strptime #121237
Description
Bug report
Bug description:
https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes documents "strftime() and strptime() Format Codes". It mentions the new %:z variant of %z, introduced in Python 3.12
>>> datetime.datetime.strptime("2023-07-17T13:58:49-07:00", "%Y-%m-%dT%H:%M:%S%z")
datetime.datetime(2023, 7, 17, 13, 58, 49, tzinfo=datetime.timezone(datetime.timedelta(days=-1, seconds=61200)))
>>> datetime.datetime.strptime("2023-07-17T13:58:49-07:00", "%Y-%m-%dT%H:%M:%S%:z")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.12/_strptime.py", line 554, in _strptime_datetime
tt, fraction, gmtoff_fraction = _strptime(data_string, format)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/_strptime.py", line 325, in _strptime
raise ValueError("'%s' is a bad directive in format '%s'" %
ValueError: ':' is a bad directive in format '%Y-%m-%dT%H:%M:%S%:z'But passing "%:z" to strptime raises an error. This is a bug because strptime and strftime should have the same format codes, according to the docs.
Since %z already parses this format when passed to strptime, I think %:z should just do the same thing.
Workaround: Change %:z to %z in your format string for strptime.
CPython versions tested on:
3.12
Operating systems tested on:
Linux
Activity
nineteendo commentedon Jul 1, 2024
Wouldn't
%:zhave to reject-0400?za3k commentedon Jul 1, 2024
Reasonable question. Shouldn't
%zreject-04:00? It doesn't, currently.Both should parse the alternative format, or neither, for the sake of consistency.
The current behavior for
%zis old (predates%:zfrom 3.12). I would argue for both to avoid breaking backwards compatibility.nineteendo commentedon Jul 1, 2024
In my view
:is optional for%z, so it's not used instrftime(), while it's required in%:z.If we enforce this, this actually allows something new instead of an alternative way to do it:
This should probably be labeled as a new feature.
za3k commentedon Jul 1, 2024
I think either implementation would be an improvement. I raise no objection :)
nineteendo commentedon Jul 1, 2024
@Eclips4 can you add the feature label?
LucasEsposito commentedon Jul 20, 2024
I'll be taking care of this one
As dicussed, we need to have consistency across
strptimeandstrftime, while keeping backwards compatibility.%zand%:zwork as expected instrftime, so no need to change anything there.%zdoes what it should instrptime, while in addition allowing%:z-formatted strings too (see third comment). We should keep this behavior for backwards compatibility.%:zfails instrptime. We should allow%:zthere and make it parse only%:z-formatted strings.pythongh-121237: Add %:z directive to strptime
pythongh-121237: Add %:z directive to strptime
LucasEsposito commentedon Jul 22, 2024
I added a PR addressing the issue: #122142
pythongh-121237: Add %:z directive to strptime
[-]Let strptime accept %:z[/-][+]Support `%:z` in `datetime.datetime.strptime`[/+]StanFromIreland commentedon Jun 29, 2025
This was implemented for strftime without consideration for strptime in 023c51d 3 years ago. I would consider this a documentation bug, since it does imply it should be available on strptime also, but implementing it is a feature now.
pythongh-121237: Add %:z directive to strptime
pythongh-121237: Add %:z directive to strptime
pythongh-121237: Add %:z directive to strptime
bn-jbischko commentedon Sep 13, 2025
Any reason why
strptimedoesn't return a datetime object with timezone, when%Zis used, either?Edit: Nevermind, see #66571
gh-121237: Add `%:z` directive to datetime.strptime (#136961)
pganssle commentedon Sep 19, 2025
This has now been implemented and merged in #136961
Iris-Hinrichs commentedon Sep 29, 2026
Although this issue has been closed and the changes seem to be implemented and merged into main I still get the same error as on top of this discussion when using python3.14 (cpython implementation). In which python release should this change be available?
Thanks for any reply on this comment!
StanFromIreland commentedon Sep 29, 2026
It was added to Python 3.15, which is to be released in two days.