date: fix timezone abbreviations using wrong offset outside their DST season#11045
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cakebaker merged 1 commit intouutils:mainfrom Feb 21, 2026
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This supersedes #11043 (MEZ/MESZ only) with a broader fix. The simpler PR is there as a fallback if this refactor needs more discussion. |
Merging this PR will improve performance by 8.91%
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EDT/PDT/CDT/MDT were being mapped to IANA region names (e.g. EDT →
America/New_York), which meant
dt.to_zoned(tz)would pick whateveroffset the region has on that date. So "10:00 EDT" in January would
resolve to UTC-5 (EST) instead of UTC-4, because New York is in
standard time in winter. But EDT means UTC-4, always — the abbreviation
itself says it's daylight time.
Replaced
PREFERRED_TZ_MAPPINGSwithFIXED_OFFSET_ABBREVIATIONSthatstores the actual UTC offset in seconds for each abbreviation. Seconds
instead of hours because IST is UTC+5:30 and ACST is UTC+9:30. The
dynamic IANA database fallback is still there for anything not in the
static table.
Also adds MEZ/MESZ while I was in there (fixes #11015).
Ref: https://data.iana.org/time-zones/theory.html
Ref: https://www.rfc-editor.org/rfc/rfc9557.html#section-2
Fixes #10805
Fixes #11015