Summary

get_timezone_gmt renders 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):

>>> from datetime import datetime
>>> from babel.dates import get_timezone, get_timezone_gmt
>>> tz = get_timezone('America/St_Johns')
>>> dt = datetime(2007, 1, 1, 12, 0, tzinfo=tz)
>>> get_timezone_gmt(dt, locale='en')
'GMT-04:30'          # should be 'GMT-03:30'
>>> get_timezone_gmt(dt, 'short', locale='en')
'-0430'              # should be '-0330'

Pacific/Marquesas (UTC-09:30) is likewise rendered as GMT-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:

>>> divmod(-12600, 3600)   # -3:30 in seconds
(-4, 1800)

The code printed the floored hour (-4) via %+03d while taking the minutes from the positive remainder (1800 // 60 == 30), producing -04:30 for a -03:30 offset.

Fix

Decompose the offset from its absolute value and track the sign separately (the same idiom the code already uses elsewhere):

sign = '-' if seconds < 0 else '+'
hours, seconds = divmod(abs(seconds), 3600)

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' whenever 0 <= hours < 100. I verified this exhaustively across all offsets from -12:00 to +14:00 in 15-minute steps and all four widths (plus return_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 the pytz and zoneinfo backends). They fail before the change (AssertionError: assert 'GMT-04:30' == 'GMT-03:30') and pass after, on both backends.

Happy to add a CHANGES.rst bugfix entry if you would like one included in this PR rather than compiled at release time.