python / python/cpython

`date.strftime` and `datetime.strftime` format dates wrong in some locales.

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3.13 extension-modules OS-windows stdlib type-bug
Dominant language
Python
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Description

Bug report

Bug description:

date.strftime and datetime.strftime format dates wrong in some locales. For example, when the locale is Bulgaria the '%A' format string returns an incorrect value.

>>> locale.setlocale(locale.LC_TIME, 'bg')    # 'bg' is Bulgaria
>>> date_str = datetime.date(2025, 2, 25).strftime('%A') # %A is locale's day of the week
>>> date_str
'âòîðíèê'
>>> date_str.encode('cp1252').decode('cp1251')  # I think we're interpreting a cp1251 string as cp1252
'вторник'  # Google tells me this is Tuesday in Bulgarian

This also fails with the '%x' format string

I've only tested this on Windows.

My guess is that CPython is making a narrow character API call and using the wrong code page. It should be using the wide character call instead.

CPython versions tested on:

3.13

Operating systems tested on:

Windows

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Research direction

Reproduce the issue on Windows using date.strftime and datetime.strftime with the Bulgarian locale, checking both the %A and %x format strings. Trace how these entry points obtain locale-formatted text and verify that the result is the correctly decoded Bulgarian value rather than mojibake.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
localization
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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