[faresrafat3]

Summary

pendulum.now() crashed with TypeError: 'None' is not an instance of 'str'
when /etc/localtime is a bare copy of a zoneinfo file (minimal containers,
Slurm jobs). _get_unix_timezone returned a Timezone whose key is None,
and the Rust precise_diff helper assumed the key is a str.

Root cause: _get_unix_timezone falls through to Timezone.from_file(f) when
no named configuration is found. A zoneinfo file without an IANA key yields a
Timezone with key is None. precise_diff then calls get_tz_name, which
casts that None to PyString and raises.

Verification

$ python3.12 -c "import pendulum; from io import BytesIO; import pendulum.tz.timezone as t; d=open('/tmp/scratchpad/pendulum-src/tests/fixtures/tz/Paris','rb').read(); tz=t.Timezone.from_file(BytesIO(d)); a=pendulum.now(tz); b=pendulum.now(tz); print(b-a)"
TypeError: 'None' is not an instance of 'str'

$ PYTHONPATH=src python3.12 -m pytest tests/tz/ -q
641 passed, 3 skipped, 1 warning

Fix

When the bare-file fallback yields a keyless Timezone, fall through to the
existing UTC default (with the existing warning) instead of returning it.
Timezone.from_file itself still allows a keyless result for pickling and
utcoffset use, so test_from_file_without_a_key_can_be_pickled still
passes. _tz_from_env now passes the file path as the key so that path never
produces a keyless Timezone.

New test test_unix_localtime_regular_file_defaults_to_utc builds a root with
/etc/localtime as a regular file and asserts the resolver returns a named
(UTC) timezone. Against the unfixed code this test fails (resolver returns
the keyless Timezone).

What I did not verify

• Timezone.from_file(f) called directly with no key still produces a
  keyless Timezone; precise_diff against it still crashes in the Rust
  extension. A one-line guard in rust/src/python/helpers.rs (get_tz_name:
  return an empty string when the key is None) would close that path and
  preserve the local offset; I did not build the Rust extension (no cargo
  on this machine) so that guard is not included here.
• The change makes the Slurm case report UTC rather than the container's
  real offset. That matches the reporter's own workaround
  (pendulum.now('UTC')); preserving the offset needs the Rust guard above.

Pull Request Check List

• Added tests for changed code.
• Updated documentation for changed code.

Fixes #989.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has insufficient remaining quota. Try requesting a review at a lower effort level.