[issue40503] PEP 615: Add zoneinfo module

[Steve Dower]

Steve Dower  added the comment:

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.

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[issue40503] PEP 615: Add zoneinfo module

[Isuru Fernando]

Isuru Fernando  added the comment:

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.

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[issue40503] PEP 615: Add zoneinfo module

[Steve Dower]

Steve Dower  added the comment:

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.

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[issue40503] PEP 615: Add zoneinfo module

[Isuru Fernando]

Isuru Fernando  added the comment:

Thanks @steve.dower for the info. I've created 
https://github.com/python/cpython/pull/28495. Let me know if it needs to have a 
separate bpo issue.

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[issue40503] PEP 615: Add zoneinfo module

[Isuru Fernando]

Change by Isuru Fernando :


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pull_requests: +26890
pull_request: https://github.com/python/cpython/pull/28495

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[issue40503] PEP 615: Add zoneinfo module

[STINNER Victor]

Change by STINNER Victor :


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[issue40503] PEP 615: Add zoneinfo module

[Steve Dower]

Steve Dower  added the comment:

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.

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[issue40503] PEP 615: Add zoneinfo module

[Isuru Fernando]

Isuru Fernando  added the comment:

> If anyone building Python for Windows shows up needing support for this, we 
> can re-visit the issue — I don't believe it's technically infeasible, just 
> that the usage patterns of Python on Windows mean that it's not worth doing.

At conda-forge, we need this and our current solution is
https://github.com/conda-forge/python-feedstock/blob/8195ba1178041b7461238e8c5680eee62f5ea9d0/recipe/patches/0032-Fix-TZPATH-on-windows.patch#L19

I can change to check if that directory exists. What do you think?

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[issue40503] PEP 615: Add zoneinfo module

[STINNER Victor]

STINNER Victor  added the comment:

I suggest to open a separated issue to discuss how tzdata can be installed on 
Travis CI, Azure Pipelines, Buildbots, etc. when running tests.

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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

Paul Ganssle  added the comment:


New changeset b17e49e0def23238b9e7f48c8a02e2d7bbf1f653 by Paul Ganssle in 
branch 'master':
bpo-40503: Add documentation and what's new entry for zoneinfo (GH-20006)
https://github.com/python/cpython/commit/b17e49e0def23238b9e7f48c8a02e2d7bbf1f653


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[issue40503] PEP 615: Add zoneinfo module

[STINNER Victor]

STINNER Victor  added the comment:


New changeset 62972d9d73e83d6eea157617cc69500ffec9e3f0 by Paul Ganssle in 
branch 'master':
bpo-40503: PEP 615: Tests and implementation for zoneinfo (GH-19909)
https://github.com/python/cpython/commit/62972d9d73e83d6eea157617cc69500ffec9e3f0


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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

Paul Ganssle  added the comment:

Talked to Steve Dower in a sidebar about the issue with compile-time 
configuration, he is convinced that compile-time configuration is not something 
that would be useful or worth doing on Windows. I am indifferent on the matter, 
so I am fine with calling the compile-time configuration part of this done at 
this point. If anyone building Python for Windows shows up needing support for 
this, we can re-visit the issue — I don't believe it's technically infeasible, 
just that the usage patterns of Python on Windows mean that it's not worth 
doing.

So, once we've got a critical mass of reviews done for zoneinfo, I think this 
feature is done. 

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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

Paul Ganssle  added the comment:

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=50)
py_zoneinfo: mean: 2.48 µs ± 79.17 ns; min: 2.42 µs (k=5, N=10)
dateutil: mean: 10.41 µs ± 209.97 ns; min: 10.17 µs (k=5, N=5)
pytz: mean: 4.69 µs ± 252.70 ns; min: 4.39 µs (k=5, N=5)

Running to_utc in zone Europe/Paris
c_zoneinfo: mean: 539.61 ns ± 25.68 ns; min: 514.39 ns (k=5, N=50)
py_zoneinfo: mean: 2.01 µs ± 61.69 ns; min: 1.94 µs (k=5, N=10)
dateutil: mean: 7.88 µs ± 506.89 ns; min: 7.25 µs (k=5, N=5)
pytz: mean: 773.02 ns ± 14.11 ns; min: 759.56 ns (k=5, N=50)

Running utcoffset in zone Europe/Paris
c_zoneinfo: mean: 329.34 ns ± 36.31 ns; min: 302.88 ns (k=5, N=100)
py_zoneinfo: mean: 1.57 µs ± 9.58 ns; min: 1.55 µs (k=5, N=20)
dateutil: mean: 6.28 µs ± 86.61 ns; min: 6.16 µs (k=5, N=5)
pytz: mean: 461.47 ns ± 2.07 ns; min: 458.91 ns (k=5, N=50)


`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).

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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

Paul Ganssle  added the comment:

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.

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[issue40503] PEP 615: Add zoneinfo module

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Do we need the C implementation if there is the Python implementation?

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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

Paul Ganssle  added the comment:

Thanks Thomas, that was super helpful. I've created GH-20034 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.

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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

Change by Paul Ganssle :


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pull_request: https://github.com/python/cpython/pull/20034

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[issue40503] PEP 615: Add zoneinfo module

[Thomas Wouters]

Thomas Wouters  added the comment:

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.

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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

Paul Ganssle  added the comment:

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.

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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

Change by Paul Ganssle :


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pull_requests: +19318
pull_request: https://github.com/python/cpython/pull/20006

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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

Change by Paul Ganssle :


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keywords: +patch
pull_requests: +19224
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/19909

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[issue40503] PEP 615: Add zoneinfo module

[Paul Ganssle]

New submission from Paul Ganssle :

This is an issue to track the implementation of PEP 615: 
https://www.python.org/dev/peps/pep-0615/

It should mostly involve migrating from the reference implementation: 
https://github.com/pganssle/zoneinfo/

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assignee: p-ganssle
components: Library (Lib)
messages: 368076
nosy: belopolsky, lemburg, p-ganssle
priority: high
severity: normal
stage: needs patch
status: open
title: PEP 615: Add zoneinfo module
type: enhancement
versions: Python 3.9

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