gh-93099: Fix _pyio to use locale module properly (gh-93136)

(cherry picked from commit f7fabae75c)

Co-authored-by: Dong-hee Na <donghee.na@python.org>

Lib/_pyio.py

@@ -2022,13 +2022,7 @@ class TextIOWrapper(TextIOBase):
         encoding = text_encoding(encoding)
 
         if encoding == "locale":
-            try:
-                import locale
-            except ImportError:
-                # Importing locale may fail if Python is being built
-                encoding = "utf-8"
-            else:
-                encoding = locale.getencoding()
+            encoding = self._get_locale_encoding()
 
         if not isinstance(encoding, str):
             raise ValueError("invalid encoding: %r" % encoding)
@@ -2162,7 +2156,7 @@ class TextIOWrapper(TextIOBase):
             if not isinstance(encoding, str):
                 raise TypeError("invalid encoding: %r" % encoding)
             if encoding == "locale":
-                encoding = locale.getencoding()
+                encoding = self._get_locale_encoding()
 
         if newline is Ellipsis:
             newline = self._readnl
@@ -2267,6 +2261,15 @@ class TextIOWrapper(TextIOBase):
         self._decoded_chars_used += len(chars)
         return chars
 
+    def _get_locale_encoding(self):
+        try:
+            import locale
+        except ImportError:
+            # Importing locale may fail if Python is being built
+            return "utf-8"
+        else:
+            return locale.getencoding()
+
     def _rewind_decoded_chars(self, n):
         """Rewind the _decoded_chars buffer."""
         if self._decoded_chars_used < n:

Lib/test/test_io.py

@@ -3570,6 +3570,10 @@ class TextIOWrapperTest(unittest.TestCase):
         F.tell = lambda x: 0
         t = self.TextIOWrapper(F(), encoding='utf-8')
 
+    def test_reconfigure_locale(self):
+        wrapper = io.TextIOWrapper(io.BytesIO(b"test"))
+        wrapper.reconfigure(encoding="locale")
+
     def test_reconfigure_encoding_read(self):
         # latin1 -> utf8
         # (latin1 can decode utf-8 encoded string)