From: Petr Viktorin <encukou@gmail.com>
Date: Wed, 13 Aug 2025 07:03:05 +0000 (+0200)
Subject: gh-131146: Fall back to `month_name` if `standalone_month_name`s aren't distinct... 
X-Git-Tag: v3.15.0a1~706
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=639df39bf0b7e1172ebc4df84c1ae097ea7c0c22;p=thirdparty%2FPython%2Fcpython.git

gh-131146: Fall back to `month_name` if `standalone_month_name`s aren't distinct (GH-137674)

Some systems reportedly don't expand '%OB' and '%Ob'.
In this case (and similar theoretically possible ones, like expanding to empty
string or 'OB'), fall back to the month_name & month_abbr.
---

diff --git a/Lib/calendar.py b/Lib/calendar.py
index 45bb265a6560..fd6c561a9d39 100644
--- a/Lib/calendar.py
+++ b/Lib/calendar.py
@@ -149,6 +149,14 @@ try:
 except ValueError:
     standalone_month_name = month_name
     standalone_month_abbr = month_abbr
+else:
+    # Some systems that do not support '%OB' will keep it as-is (i.e.,
+    # we get [..., '%OB', '%OB', '%OB']), so for non-distinct names,
+    # we fall back to month_name/month_abbr.
+    if len(set(standalone_month_name)) != len(set(month_name)):
+        standalone_month_name = month_name
+    if len(set(standalone_month_abbr)) != len(set(month_abbr)):
+        standalone_month_abbr = month_abbr
 
 
 def isleap(year):