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Consider testing zoneinfo with tzdata PyPI package installed #99649

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Consider testing zoneinfo with tzdata PyPI package installed#99649
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infraCI, GitHub Actions, buildbots, Dependabot, etc.testsTests in the Lib/test dirtype-featureA feature request or enhancement

Description

@sobolevn
sobolevn
opened on Nov 21, 2022

Feature or enhancement

Right now none of our build bots test zoneinfo with tzdata pypi package installed.
Proof: https://github.com/python/cpython/pull/99602/files#diff-7908b1930bd1135d6f8077ef5ff578b02577f5f7042b54be88b9b86b6c7af45dR27-R35

Link to the package: https://pypi.org/project/tzdata/

However, it works locally:

(.venv) ~/Desktop/cpython  issue-99508 ✔                                             
» pip install tzdata     
Collecting tzdata
  Using cached tzdata-2022.6-py2.py3-none-any.whl (338 kB)
Installing collected packages: tzdata
Successfully installed tzdata-2022.6

(.venv) ~/Desktop/cpython  issue-99508 ✔                                             
» python
Python 3.12.0a2+ (heads/main:a3360facba, Nov 19 2022, 14:10:54) [Clang 11.0.0 (clang-1100.0.33.16)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import importlib.metadata
>>> importlib.metadata.metadata("tzdata")
<importlib.metadata._adapters.Message object at 0x107d5df50>

But, presence / absence of this 3rd party package change the behavior of zoneinfo module: both C and Python versions of it.

So, we need to be sure that tests can check all combinations.

Risks

Right now we don't have 3rd party packages installed for tests.
This might cause quite a lot of problems: where / how / when to install it.
It also can affect test / buildbot stability, because pip sometimes just fails to install some packages and you have to retry.

Pitch

I think we should test with tzdata PyPI package installed on at least one buildbot / CI job.
The question is: how can we do it without compromising the CI setup and reliability?

Previous discussion

CC @pganssle

Activity

  1. sobolevn
    added
    type-featureA feature request or enhancement
    testsTests in the Lib/test dir
    buildThe build process and cross-build
    on Nov 21, 2022

  2. vstinner commented on Nov 21, 2022

    @vstinner
    vstinner
    on Nov 21, 2022
    Member

    In general, I dislike that Python test suite depends on an external resources. It makes tests more error prone :-( Is it possible to mock the 3rd party tzdata package in tests?

  3. sobolevn commented on Nov 21, 2022

    @sobolevn
    sobolevn
    on Nov 21, 2022
    MemberAuthor

    In general, I dislike that Python test suite depends on an external resources.

    Yes, me too. I guess this can also set a bad precedent: other 3rd-party libs can be added after that as well.

    Is it possible to mock the 3rd party tzdata package in tests?

    I was thinking about something similar. Maybe storing some old version of it in test_zoneinfo/ test package and run tests twice: with and without it.

    No idea how hard it would be, because I've never seen what's inside tzdata package 🤔

  4. vstinner commented on Nov 21, 2022

    @vstinner
    vstinner
    on Nov 21, 2022
    Member

    I'm not talking about an hypothetical issue. For 3 weeks, I'm getting tons of email because some buildbots fail to download data from unicode.org, and so test_unicodedata fails randomly. I qualify these issues as "network issue". It happens a lot.

    Browse https://mail.python.org/archives/list/buildbot-status@python.org/ and search for "test_unicodedata".

    Example: https://buildbot.python.org/all/#/builders/662/builds/960

    test_normalization (test.test_unicodedata.NormalizationTest) ... 	fetching http://www.pythontest.net/unicode/13.0.0/NormalizationTest.txt ...
FAIL

======================================================================
FAIL: test_normalization (test.test_unicodedata.NormalizationTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/http/client.py", line 587, in _read_chunked
    value.append(self._safe_read(amt))
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/http/client.py", line 632, in _safe_read
    raise IncompleteRead(data, amt-len(data))
http.client.IncompleteRead: IncompleteRead(7631 bytes read, 561 more expected)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/test/test_unicodedata.py", line 343, in test_normalization
    testdata = open_urlresource(TESTDATAURL, encoding="utf-8",
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/test/support/__init__.py", line 596, in open_urlresource
    s = f.read()
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/gzip.py", line 301, in read
    return self._buffer.read(size)
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/_compression.py", line 118, in readall
    while data := self.read(sys.maxsize):
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/gzip.py", line 494, in read
    buf = self._fp.read(io.DEFAULT_BUFFER_SIZE)
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/gzip.py", line 88, in read
    return self.file.read(size)
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/http/client.py", line 459, in read
    return self._read_chunked(amt)
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/http/client.py", line 597, in _read_chunked
    raise IncompleteRead(b''.join(value))
http.client.IncompleteRead: IncompleteRead(0 bytes read)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.10.cstratak-fedora-rawhide-ppc64le.clang/build/Lib/test/test_unicodedata.py", line 349, in test_normalization
    self.fail(f"Could not retrieve {TESTDATAURL}")
AssertionError: Could not retrieve http://www.pythontest.net/unicode/13.0.0/NormalizationTest.txt

  5. FFY00 commented on Dec 15, 2022

    @FFY00
    FFY00
    on Dec 15, 2022
    Member

    As per my reply in #99602 (comment), we don't need the tzdata package. It exists as a way to support data lookup when system provided tzdata is not available. We don't actually need it to test the code that loads the tzdata that way, it can be mocked. The only reason to add it would be for an integration test, which I am under the impression it's not that common here, and I don't think it's really needed, especially considering the tzdata PyPI package just repackages the tzdata from IANA, the upstream, (https://github.com/python/tzdata/blob/master/update.py) and we already test with the system provided tzdata.

  6. hugovk commented on Jun 23, 2023

    @hugovk
    hugovk
    on Jun 23, 2023
    Member

    PR #19909 added Misc/requirements-test.txt and installed it as part of .github/workflows/coverage.yml and .travis.yml.

    However, PRs #25679 and #30257 removed those CI files, so Misc/requirements-test.txt is unused.

    Should we install it as part of another GitHub Actions workflow? (Replies on this issue suggest not.) Should we remove it?

  7. hugovk commented on Oct 2, 2023

    @hugovk
    hugovk
    on Oct 2, 2023
    Member

    Yes, let's remove Misc/requirements-test.txt. Please see PR #110240.

  8. FFY00 commented on Oct 13, 2023

    @FFY00
    FFY00
    on Oct 13, 2023
    Member

    @sobolevn do you think adding a test for zonoinfo._common.load_tzdata using mocks would be enough?

    I think we should add a test for zonoinfo._common.load_tzdata with mocks regardless, so that it can still be tested when the tzdata package is missing. We can then also add a test using the tzdata package, if anyone thinks it is necessary — for me, it'd be a nice to have, but probably not worth the effort on the CI maintenance.

  9. StanFromIreland
    added this to Date and time issues 🕰️on Jun 30, 2025
  10. StanFromIreland
    removed
    buildThe build process and cross-build
    on Jul 7, 2025
  11. StanFromIreland
    added
    infraCI, GitHub Actions, buildbots, Dependabot, etc.
    on Aug 18, 2025

  12. StanFromIreland commented on Oct 2, 2025

    @StanFromIreland
    StanFromIreland
    on Oct 2, 2025
    Member

    Note that this would require installing tzdata 2020a (or 2020b, the tests still pass, 2021a introduces six failures), since that is what our extract was compiled with:

    cpython/Lib/test/test_zoneinfo/data/zoneinfo_data.json

    Line 188 in 8797e1a

    "version": "2020a"

  13. originaonxi commented on Feb 4, 2026

    @originaonxi
    originaonxi
    on Feb 4, 2026 · Hidden as off-topic

  14. StanFromIreland commented on Feb 4, 2026

    @StanFromIreland
    StanFromIreland
    on Feb 4, 2026 · Hidden as resolved

  15. StanFromIreland commented on Feb 21, 2026

    @StanFromIreland
    StanFromIreland
    on Feb 21, 2026
    Member

    I set up my buildbot to cover this (and all other tests that require the 'tzdata' resource).

  16. StanFromIreland
    closed this as completedon Feb 21, 2026
  17. github-project-automation
    moved this to Done in Date and time issues 🕰️on Feb 21, 2026
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