TST: tzdata is a required dependency when testing

[simonjayhawkins]

Nightlies are sadly still broken.
On Windows, the failures are because tzdata is a required dependency when testing, because of a bug here.

pandas/pandas/conftest.py

Lines 1219 to 1220 in 259a15c

	if zoneinfo is not None:
	TIMEZONES.extend([zoneinfo.ZoneInfo("US/Pacific"), zoneinfo.ZoneInfo("UTC")])

We need to create a dummy ZoneInfo object and check to see if that works as zoneinfo will not raise if tzdata is missing on import, only when creating the ZoneInfo object.

tzdata should also probably be added to the optional dependencies list in the docs and in pandas/compat/_optional.py.
I dunno which minimum version we should support though.

cc @jbrockmendel (who added zoneinfo support)

Originally posted by @lithomas1 in #46856 (comment)

[jbrockmendel]

We need to create a dummy ZoneInfo object and check to see if that works as zoneinfo will not raise if tzdata is missing on import, only when creating the ZoneInfo object.

Would making tzdata required solve the issue? Seems easier.

[simonjayhawkins]

for the nightlies to upload, will just skip the test for now (on https://github.com/MacPython/pandas-wheels). If tests fail the wheel upload to staging is bypassed.

[simonjayhawkins]

will just skip the test for now (on https://github.com/MacPython/pandas-wheels).

talking rubbish. Fails with ImportError while loading conftest 'D:\a\1\s\test_venv\lib\site-packages\pandas\conftest.py'. we can skip tests on pandas-wheels, but we don't patch pandas. Should fix here, but can maybe add tzdata to the setup script there for now.

[simonjayhawkins]

added tzdata to TEST_DEPENDS for windows env for now. MacPython/pandas-wheels#185

issue remains open to fix in pandas so that pd.test() always works.

[lithomas1]

The idea is probably to do something like

try:
    utc_zoneinfo = ZoneInfo("UTC")
except ZoneInfoNotFoundError:
    zoneinfo = None

in the conftest.
I don't have time to look into this this week, though, so someone else needs to put up a PR. Marked as blocker for rc, since min deps builds should just work.

[lithomas1]

We need to create a dummy ZoneInfo object and check to see if that works as zoneinfo will not raise if tzdata is missing on import, only when creating the ZoneInfo object.

Would making tzdata required solve the issue? Seems easier.

Slightly off topic, but is the idea to replace pytz in the future with tzdata?

[jbrockmendel]

Slightly off topic, but is the idea to replace pytz in the future with tzdata?

i suggested something similar at one point, but definitely not something decided upon