[tomasr8]

While looking into improving skeleton matching (#1084) I noticed we don't support the g date pattern (Julian day), or at least only partially. parse_pattern will accept it, but format_date raises:

>>> from babel.dates import parse_pattern, format_date
>>> from datetime import date
>>> parse_pattern('g')
<DateTimePattern 'g'>
>>> format_date(date(2000, 1, 1), 'g', locale='en')
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    format_date(date(2000, 1, 1), 'g', locale='en')
    ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/dev/babel/babel/dates.py", line 792, in format_date
    return pattern.apply(date, locale)
           ~~~~~~~~~~~~~^^^^^^^^^^^^^^
  File "~/dev/babel/babel/dates.py", line 1551, in apply
    return self % DateTimeFormat(datetime, locale, reference_date)
           ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  File "~/dev/babel/babel/dates.py", line 1543, in __mod__
    return self.format % other
           ~~~~~~~~~~~~^~~~~~~
  File "~/dev/babel/babel/dates.py", line 1616, in __getitem__
    raise KeyError(f"Unsupported date/time field {char!r}")
KeyError: "Unsupported date/time field 'g'"
>>> 

I thought it could be nice to support this pattern?

[codspeed]

Merging this PR will not alter performance

✅ 88 untouched benchmarks

---

_{Comparing tomasr8:g-date (c8510a9) with master (a18709c)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.63%. Comparing base (a18709c) to head (c8510a9).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1445   +/-   ##
=======================================
  Coverage   93.62%   93.63%           
=======================================
  Files          27       27           
  Lines        4973     4978    +5     
=======================================
+ Hits         4656     4661    +5     
  Misses        317      317           

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ubuntu-24.04-3.9	92.66% <100.00%> (+<0.01%)	⬆️
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windows-2022-3.11	92.66% <100.00%> (?)
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windows-2022-pypy3.10	92.72% <100.00%> (?)

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[tomasr8]

Just to be sure, I checked these test cases against ICU using this script:

from datetime import datetime, timezone
from icu import SimpleDateFormat, Locale, TimeZone


def format_date(pattern, tz, dt, locale='en'):
    fmt = SimpleDateFormat(pattern, Locale(locale))
    fmt.setTimeZone(TimeZone.createTimeZone(tz))
    return fmt.format(dt.timestamp())  


U = timezone.utc
print(format_date('g', 'UTC', datetime(476, 9, 4, tzinfo=U)))
print(format_date('g', 'UTC', datetime(1970, 1, 1, 12, tzinfo=U)))
print(format_date('g', 'UTC', datetime(1970, 1, 1, 12, 30, tzinfo=U)))
print(format_date('ggggggggg', 'UTC', datetime(2026, 11, 7, tzinfo=U)))

dt = datetime(2007, 3, 31, 23, 30, tzinfo=U)
print(format_date('g', 'UTC', dt))
print(format_date('g', 'Europe/Zurich', dt))

You can run it with uv:

uv run --with PyICU python

[tomasr8]

@akx do you think you could have a look when you're free? :)

[Copilot]

🟢 Approval recommended

No active review issues are recorded for the change adding g date-pattern formatting support.

No open issues 🎉

What changed in this PR

Adds formatting support for the previously accepted but unsupported g date pattern in Babel’s date and datetime formatters.

Changes:

• Calculates Julian day values from date ordinals, with zero padding based on pattern length.
• Adds tests for historical dates, ignored time components, padding, and local-time-zone behavior.
• Documents the g date field.

File	Description
tests/​test_dates.py	Tests Julian day formatting, padding, and timezone handling.
docs/​dates.rst	Replaces the g placeholder with a field description.
babel/​dates.py	Dispatches g patterns to the new Julian day formatter.

_{Review effort: Balanced}

[akx]

Well julienned! 😄

[tomasr8]

Thanks for the super quick review! ❤️