[Bug 207604] Re: pytz includes a hard coded list of time zone names

[Launchpad Bug Tracker]

This bug was fixed in the package python-tz - 2022.2.1-1ubuntu0.22.10.0

---------------
python-tz (2022.2.1-1ubuntu0.22.10.0) kinetic; urgency=medium

  * Dynamically determine list of available and common timezones (LP: #207604)
  * Determine IANA (nee Olson) database version dynamically
  * Add autopkgtests to run unittest and own regression tests

 -- Benjamin Drung <bdrung at ubuntu.com>  Tue, 21 Mar 2023 12:05:43 +0100

** Changed in: python-tz (Ubuntu Kinetic)
       Status: Fix Committed => Fix Released

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Title:
  pytz includes a hard coded list of time zone names

Status in pytz:
  New
Status in python-tz package in Ubuntu:
  Fix Released
Status in python-tz source package in Jammy:
  Fix Released
Status in python-tz source package in Kinetic:
  Fix Released

Bug description:
  [ Impact ]

  The Debian/Ubuntu packages of pytz include a patch to not install
  pytz's zoneinfo database and instead load data from the system
  zoneinfo database.  This keeps pytz up to date when system timezone
  updates are installed which is generally a good idea.

  The pytz/__init__.py includes common_timezones and all_timezones
  lists, which enumerate the time zones in the database pytz was
  released with.  If pytz is instead using the system database, these
  lists may not be correct (e.g. missing newly added time zones).

  all_timezones and common_timezones should be calculated at run time.
  all_timezones will need to use os.walk to discover what timezones
  exist. common_timezones should be loaded from zone.tab, plus a hard
  coded list of extras such as UTC and US/Eastern.

  Everytime a new timezone is added to tzdata in an update, this
  timezone cannot be used in pytz with the hardcoded list of timezones.
  For jammy and kinetic this applies to America/Ciudad_Juarez (when
  comparing pytz to tzdata 2023c). For bionic the list of missing
  timezones is even bigger:

  * America/Ciudad_Juarez
  * America/Nuuk
  * Asia/Qostanay
  * Europe/Kyiv
  * Pacific/Kanton

  [ Test Plan ]

  Two autopkgtest test cases were added:
  1. Run the upstream unittests
  2. Regression tests with all tests that I could come up with.

  There are no manual test, because all those test should also be run
  when there is a tzdata update to prevent regressions.

  To manually test, a newly added timezone to tzdata should be able to
  be specified:

  ```
  #!/usr/bin/python3
  import pytz
  pytz.timezone("America/Ciudad_Juarez")
  ```

  This should not raise UnknownTimeZoneError.

  
  [ Where problems could occur ]

  Dynamically determine the timezones relies on a correct environment
  and can fail more easily if the environment is broken. python-tz is
  used in several places (maybe in the installer). The patch might have
  a performance impact, because the list of timezones is determined
  completely (but only once) instead of constructing it lazy.

  [ Other Info ]

  Upstream recommend our approach:
  https://github.com/stub42/pytz/issues/91#issuecomment-1356628324

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