#10092: Properly reset locale in Locale*Calendar classes. The context manager was buggy because setlocale() returns the *new* locale, not the old. Also add a test for this.

Doc/library/calendar.rst

@@ -170,9 +170,9 @@ it's the base calendar for all computations.
 .. class:: LocaleTextCalendar(firstweekday=0, locale=None)
 
    This subclass of :class:`TextCalendar` can be passed a locale name in the
-   constructor and will return month and weekday names in the specified
-   locale. If this locale includes an encoding all strings containing month and
-   weekday names will be returned as unicode.
+   constructor and will return month and weekday names in the specified locale.
+   If this locale includes an encoding all strings containing month and weekday
+   names will be returned as unicode.
 
 
 .. class:: LocaleHTMLCalendar(firstweekday=0, locale=None)
@@ -182,6 +182,12 @@ it's the base calendar for all computations.
    locale. If this locale includes an encoding all strings containing month and
    weekday names will be returned as unicode.
 
+.. note::
+
+   The :meth:`formatweekday` and :meth:`formatmonthname` methods of these two
+   classes temporarily change the current locale to the given *locale*.  Because
+   the current locale is a process-wide setting, they are not thread-safe.
+
 
 For simple text calendars this module provides the following functions.
 

Lib/calendar.py

@@ -486,8 +486,8 @@ class different_locale:
         self.locale = locale
 
     def __enter__(self):
-        self.oldlocale = _locale.setlocale(_locale.LC_TIME, self.locale)
-        #return _locale.getlocale(_locale.LC_TIME)[1]
+        self.oldlocale = _locale.getlocale(_locale.LC_TIME)
+        _locale.setlocale(_locale.LC_TIME, self.locale)
 
     def __exit__(self, *args):
         _locale.setlocale(_locale.LC_TIME, self.oldlocale)

Lib/test/test_calendar.py

@@ -3,6 +3,7 @@ import unittest
 
 from test import support
 import time
+import locale
 
 result_2004_text = """
                                   2004
@@ -250,6 +251,22 @@ class CalendarTestCase(unittest.TestCase):
             # verify it "acts like a sequence" in two forms of iteration
             self.assertEqual(value[::-1], list(reversed(value)))
 
+    def test_localecalendars(self):
+        # ensure that Locale{Text,HTML}Calendar resets the locale properly
+        # (it is still not thread-safe though)
+        try:
+            def_locale = locale.getdefaultlocale()
+        except locale.Error:
+            # cannot determine a default locale -- skip test
+            return
+        old_october = calendar.TextCalendar().formatmonthname(2010, 10, 10)
+        calendar.LocaleTextCalendar(
+            locale=def_locale).formatmonthname(2010, 10, 10)
+        calendar.LocaleHTMLCalendar(
+            locale=def_locale).formatmonthname(2010, 10)
+        new_october = calendar.TextCalendar().formatmonthname(2010, 10, 10)
+        self.assertEquals(old_october, new_october)
+
 
 class MonthCalendarTestCase(unittest.TestCase):
     def setUp(self):

Misc/NEWS

@@ -34,6 +34,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #10092: Properly reset locale in calendar.Locale*Calendar classes.
+
 - logging: Added _logRecordClass, getLogRecordClass, setLogRecordClass to
   increase flexibility of LogRecord creation.