Fix get_timezone_gmt hour for negative fractional offsets - #1291
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Fix get_timezone_gmt hour for negative fractional offsets#1291vineethsaivs wants to merge 1 commit into
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For a timezone whose UTC offset has a non-zero minute part and is negative (for example America/St_Johns at UTC-03:30), get_timezone_gmt rendered the hour one step too far from zero, producing 'GMT-04:30' instead of 'GMT-03:30'. divmod() on a negative number floors the quotient and returns a non-negative remainder, so divmod(-12600, 3600) is (-4, 1800): the code printed the floored hour -4 while taking the minutes from the positive remainder. Decompose the offset from its absolute value and track the sign separately. For every offset that already formatted correctly the output is unchanged, because '%s%02d' with the explicit sign matches '%+03d' whenever 0 <= hours < 100.
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akx
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Jul 30, 2026
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One small change request so we do a little less work for the Z case.
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| sign = '-' if seconds < 0 else '+' | ||
| hours, seconds = divmod(abs(seconds), 3600) | ||
| if return_z and hours == 0 and seconds == 0: | ||
| return 'Z' |
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While we're at it, let's move this check higher up, before we do the sign and divmod dance:
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| sign = '-' if seconds < 0 else '+' | |
| hours, seconds = divmod(abs(seconds), 3600) | |
| if return_z and hours == 0 and seconds == 0: | |
| return 'Z' | |
| if return_z and seconds == 0: | |
| return 'Z' | |
| sign = '-' if seconds < 0 else '+' | |
| hours, seconds = divmod(abs(seconds), 3600) |
| else: | ||
| pattern = locale.zone_formats['gmt'] % '%+03d:%02d' | ||
| return pattern % (hours, seconds // 60) | ||
| pattern = locale.zone_formats['gmt'] % '%s%02d:%02d' |
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Just for my own record: over all of the locales we have now, zone_formats["gmt"]s are
Counter({'GMT%s': 937, 'UTC%s': 53, 'غرينتش%s': 29, 'GMT %s': 25, '𞤑𞤖𞤘%s': 13, 'जीएमटी%s': 4, '%s GMT': 4, 'MAG%s': 3, 'ᱡᱤᱮᱢᱴᱤ%s': 3, 'WAT%s': 3, '%s گرینویچ': 3, 'জি এম টি %s': 3, 'گرینیچ %s': 3, 'TMG%s': 2, 'जी.एम.टी. %s': 2, '𐐘𐐣𐐓 %s': 2, '%s Gk': 2, 'ម៉ោង\u200bសកល %s': 2, '[GMT]%s': 2, 'ग्री॰ मै॰ टै॰%s': 2, '·𐑜𐑥𐑑%s': 2, 'Гринуич%s': 2, 'जि.एम.ति %s': 2, 'ꋧꃅꎕꏦꄮꈉ%s': 2, 'ߜ߭ߕߖ%s': 2, 'जी एम टी %s': 2, 'tenpo UTC%s': 2, 'ཇི་ཨེམ་ཏི་%s': 2, 'ጂ ኤም ቲ%s': 2, 'GMT%s\u200e': 2, 'ග්\u200dරිමවේ%s': 2, 'ജിഎംടി %s': 2})so this'll work as before.
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Summary
get_timezone_gmtrenders the wrong hour for any timezone whose UTC offset has a non-zero minute part and is negative. For example, Newfoundland Standard Time (America/St_Johns, UTC-03:30):Pacific/Marquesas(UTC-09:30) is likewise rendered asGMT-10:30. Positive fractional offsets (Asia/Kolkata,+05:30) and whole-hour negatives (America/Los_Angeles,-08:00) are correct, so this is specific to negative offsets with minutes. Newfoundland Time covers a real, populated region, so this is user-facing incorrect output.Root cause
divmod()on a negative value floors the quotient and returns a non-negative remainder:The code printed the floored hour (
-4) via%+03dwhile taking the minutes from the positive remainder (1800 // 60 == 30), producing-04:30for a-03:30offset.Fix
Decompose the offset from its absolute value and track the sign separately (the same idiom the code already uses elsewhere):
and emit the sign explicitly (
'%s%02d...') instead of relying on'%+03d'.For every offset that already formatted correctly the output is unchanged:
'%s%02d'with the explicit sign is byte-identical to'%+03d'whenever0 <= hours < 100. I verified this exhaustively across all offsets from -12:00 to +14:00 in 15-minute steps and all four widths (plusreturn_z): the new code differs from the old in exactly the negative-fractional cases and nowhere else.Tests
Added three assertions to the existing
test_get_timezone_gmt(already parametrized over both thepytzandzoneinfobackends). They fail before the change (AssertionError: assert 'GMT-04:30' == 'GMT-03:30') and pass after, on both backends.Happy to add a
CHANGES.rstbugfix entry if you would like one included in this PR rather than compiled at release time.