time.strptime's caching of its locale object was being recreated when the

locale changed but not used during the function call it was recreated during.

The test in this checkin is untested (OS X does not have the proper locale
support for me to test), although the fix for the bug this deals with
was tested by the OP (#1290505).  Once the buildbots verify the test at least
doesn't fail it becomes a backport candidate.

Lib/_strptime.py

@@ -295,17 +295,16 @@ def strptime(data_string, format="%a %b %d %H:%M:%S %Y"):
     """Return a time struct based on the input string and the format string."""
     global _TimeRE_cache, _regex_cache
     with _cache_lock:
-        time_re = _TimeRE_cache
-        locale_time = time_re.locale_time
-        if _getlang() != locale_time.lang:
+        if _getlang() != _TimeRE_cache.locale_time.lang:
             _TimeRE_cache = TimeRE()
-            _regex_cache = {}
+            _regex_cache.clear()
         if len(_regex_cache) > _CACHE_MAX_SIZE:
             _regex_cache.clear()
+        locale_time = _TimeRE_cache.locale_time
         format_regex = _regex_cache.get(format)
         if not format_regex:
             try:
-                format_regex = time_re.compile(format)
+                format_regex = _TimeRE_cache.compile(format)
             # KeyError raised when a bad format is found; can be specified as
             # \\, in which case it was a stray % but with a space after it
             except KeyError, err:

Lib/test/test_strptime.py

@@ -505,6 +505,23 @@ class CacheTests(unittest.TestCase):
         self.failIfEqual(locale_time_id,
                          id(_strptime._TimeRE_cache.locale_time))
 
+    def test_TimeRE_recreation(self):
+        # The TimeRE instance should be recreated upon changing the locale.
+        locale_info = locale.getlocale(locale.LC_TIME)
+        try:
+            locale.setlocale(locale.LC_TIME, ('en_US', 'UTF8'))
+        except locale.Error:
+            return
+        try:
+            _strptime.strptime('10', '%d')
+            first_time_re_id = id(_strptime._TimeRE_cache)
+            locale.setlocale(locale.LC_TIME, ('de_DE', 'UTF8'))
+            _strptime.strptime('10', '%d')
+            second_time_re_id = id(_strptime._TimeRE_cache)
+            self.failIfEqual(first_time_re_id, second_time_re_id)
+        finally:
+            locale.setlocale(locale.LC_TIME, locale_info)
+
 
 def test_main():
     test_support.run_unittest(

Misc/NEWS

@@ -200,6 +200,9 @@ Core and builtins
 Library
 -------
 
+- Bug #1290505: time.strptime's internal cache of locale information is now
+  properly recreated when the locale is changed.
+
 - Patch #1685563: remove (don't add) duplicate paths in distutils.MSVCCompiler.
 
 - Added a timeout parameter to the constructor of other protocols