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PEP 615: Add zoneinfo module #84683Description
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assignee = 'https://github.com/pganssle'
closed_at = None
created_at = <Date 2020-05-04.18:51:21.137>
labels = ['type-feature', 'library', '3.9']
title = 'PEP 615: Add zoneinfo module'
updated_at = <Date 2021-09-21.20:27:37.648>
user = 'https://github.com/pganssle' bugs.python.org fields:
activity = <Date 2021-09-21.20:27:37.648>
actor = 'steve.dower'
assignee = 'p-ganssle'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-05-04.18:51:21.137>
creator = 'p-ganssle'
dependencies = []
files = []
hgrepos = []
issue_num = 40503
keywords = ['patch']
message_count = 17.0
messages = ['368076', '368461', '368619', '368634', '368649', '368656', '368658', '368800', '369021', '369059', '369206', '401992', '402247', '402330', '402350', '402352', '402357']
nosy_count = 8.0
nosy_names = ['lemburg', 'twouters', 'belopolsky', 'serhiy.storchaka', 'steve.dower', 'p-ganssle', 'isuruf', 'FFY00']
pr_nums = ['19909', '20006', '20034', '28495']
priority = 'high'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40503'
versions = ['Python 3.9'] Activitypganssle commented on May 4, 2020 pganssle commented on May 8, 2020 I've separated this into two separate PRs, one for docs and one for tests/implementation.
I have not yet implemented the logic for the ability to configure the TZPATH at compile time because I'm not quite sure how to start on that. How are other compile-time options implemented? Do I need to do something special to handle both Windows and POSIX systems? Is there already a configuration file somewhere that I should use for this? Adding Thomas to the nosy list because he's the only one listed for "autoconf/makefiles" – don't know if that extends to the Windows build as well. Yhg1s commented on May 11, 2020 The normal way to do this (for make/autoconf) is to add a --with-tzpath argument to configure.ac, and a make variable to pass it to the compilation of anything that needs it. You can then access it from Python code with sysconfig.get_config_var().
In configure.ac, AC_SUBST(TZPATH) makes configure replace @TZPATH@ in the Makefile with the value you set to $TZPATH in configure.ac. You then either add that to the global PY_CFLAGS_NODIST, or modify the build rule for the module that needs it to pass it along. (See for example how GITTAG/GITVERSION/GITBRANCH are passed to Modules/getbuildinfo.o.)
AC_ARG_WITH() is how you add a new --with-* argument to configure. The usual way people do this is by copying one of the other AC_ARG_WITH blocks and modifying it to suit their needs. It's a mixture of m4 and shell that can be a bit annoying to get right, but it's pretty flexible. Run autoreconf to regenerate configure. You can manually check that the shell in configure makes sense.
Something will have to be done on the Windows side as well, but I'm not sure what. Adding Steve Dower for that. pganssle commented on May 11, 2020 Thanks Thomas, that was super helpful. I've created #64233 to add in the compile-time arguments on POSIX systems at least, do you mind having a look?
For the moment I have made it non-configurable on Windows, but I think the right thing to do is to add an argument to PCbuild\build.bat. Hopefully Steve can point me in the right direction for mapping that argument (or something else) to a new config variable in sysconfig. serhiy-storchaka commented on May 11, 2020 Do we need the C implementation if there is the Python implementation? pganssle commented on May 11, 2020 I mean, theoretically we don't "need" it, but it's much, much faster, and without it nearly every operation that needs time zone offsets will be slower than pytz (which has a mechanism for caching).
Also, I've already written it, so I see no reason why not use it. pganssle commented on May 11, 2020 Here are some benchmarks run using the latest implementation. The pure Python code is pretty optimized, but the C code is still ~4-5x faster.
Running from_utc in zone Europe/Paris
c_zoneinfo: mean: 494.82 ns ± 3.80 ns; min: 489.23 ns (k=5, N=500000)
py_zoneinfo: mean: 2.48 µs ± 79.17 ns; min: 2.42 µs (k=5, N=100000)
dateutil: mean: 10.41 µs ± 209.97 ns; min: 10.17 µs (k=5, N=50000)
pytz: mean: 4.69 µs ± 252.70 ns; min: 4.39 µs (k=5, N=50000)
Running to_utc in zone Europe/Paris
c_zoneinfo: mean: 539.61 ns ± 25.68 ns; min: 514.39 ns (k=5, N=500000)
py_zoneinfo: mean: 2.01 µs ± 61.69 ns; min: 1.94 µs (k=5, N=100000)
dateutil: mean: 7.88 µs ± 506.89 ns; min: 7.25 µs (k=5, N=50000)
pytz: mean: 773.02 ns ± 14.11 ns; min: 759.56 ns (k=5, N=500000)
Running utcoffset in zone Europe/Paris
c_zoneinfo: mean: 329.34 ns ± 36.31 ns; min: 302.88 ns (k=5, N=1000000)
py_zoneinfo: mean: 1.57 µs ± 9.58 ns; min: 1.55 µs (k=5, N=200000)
dateutil: mean: 6.28 µs ± 86.61 ns; min: 6.16 µs (k=5, N=50000)
pytz: mean: 461.47 ns ± 2.07 ns; min: 458.91 ns (k=5, N=500000)
utcoffset() is very likely to be called possibly many times in certain hot loops (including implicitly as it's part of hash and equality checks).
vstinner commented on May 18, 2020 I suggest to open a separated issue to discuss how tzdata can be installed on Travis CI, Azure Pipelines, Buildbots, etc. when running tests. isuruf commented on Sep 16, 2021 zooba commented on Sep 20, 2021 That looks like a relocatable path anyway, which means you wouldn't want to compile it into the binary. Your patch to select a default value at runtime is probably better.
The compile-time option is meant for a system directory. isuruf commented on Sep 21, 2021 Thanks @steve.dower for the info. I've created #28495. Let me know if it needs to have a separate bpo issue. zooba commented on Sep 21, 2021 I meant I don't think we want that path upstream, and you should keep it as your own patch.
We don't have a "share" directory as part of CPython, but this would codify it. That would then conflict with your use of it in conda-forge.
It also makes sysconfig non-deterministic, which is going to be problematic against some other efforts around being able to treat it as static data to make native module compilation easier, as well as more generally something that often leads to security vulnerabilities and is best avoided.
So on balance, I think we will reject that patch. isuruf commented on Sep 21, 2021 Do you have a suggestion for how to make it configurable at compile time?
In POSIX platforms, we can set --with-tzpath to make it configurable at compile time. zooba commented on Sep 21, 2021 We'd need to implement some form of data store for values on Windows, which currently are not compiled in anywhere, and it would need a substitution syntax to be updated at runtime.
We're talking a big feature now, and you'd end up having just as much code on your side to make it work.
The only justification that'd make sense on our side is if we were going to bundle the tzdata file with the Windows installer, which doesn't affect you at all, apart from us then having an existing path listed that you'd want to override still. And even then, we'd probably preinstall the tzdata package which already overrides the path, and so there'd be no changes necessary to sysconfig and so we wouldn't touch it anyway. serhiy-storchaka commented on Feb 24, 2024 Should not this issue be closed? pganssle commented on Feb 25, 2024 added a commit that references this issue on Aug 6, 2025gh-84683: Check `<prefix>/share/zoneinfo` for zoneinfo files on Windo…
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