Change approach to calculate offset_to_tz_ids #207
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The previous approach relied on sampling from the current date back to a cutoff date using an arbitrary step (40 days) That meant that depending on the time of year the process run it could hit different offsets for the same timezone, leading to inconsistent results. The new approach uses pytz transition data directly which should be deterministic.
marcospri
commented
Jan 8, 2026
| ): | ||
| cutoff = datetime.datetime(self.RECENT_YEARS_START, 1, 1) | ||
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| # Find the last transition before cutoff to get the offset active at cutoff |
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I did this after finding an issue with pacific/norfolk
marcospri
commented
Jan 8, 2026
| "Asia/Nicosia", | ||
| "Asia/Qatar", | ||
| "Asia/Riyadh", | ||
| "Asia/Tbilisi", |
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I worked out a few differences in the data and it's down to these two. I can live with that.
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The previous approach relied on sampling from the current date back to a cutoff date using an arbitrary step (40 days)
That meant that depending on the time of year the process run it could hit different offsets for the same timezone, leading to inconsistent results.
The new approach uses pytz transition data directly which should be deterministic.
Found this after finding a change on the json files without any other apparent changes.
The new approach might be overkill, or at least the code is more verbose but I find "iterate over a TZ db" clearer than "step back in time 40 days at a time".
_get_latest_tz_namesalso uses the step back in time. If we merge a version of this I'll try to apply there too.