Issue #5170: Fixed regression caused when fixing #5768.

Lib/logging/__init__.py

@@ -766,7 +766,17 @@ class StreamHandler(Handler):
                 try:
                     if (isinstance(msg, unicode) and
                         getattr(stream, 'encoding', None)):
-                        stream.write(fs.decode(stream.encoding) % msg)
+                        fs = fs.decode(stream.encoding)
+                        try:
+                            stream.write(fs % msg)
+                        except UnicodeEncodeError:
+                            #Printing to terminals sometimes fails. For example,
+                            #with an encoding of 'cp1251', the above write will
+                            #work if written to a stream opened or wrapped by
+                            #the codecs module, but fail when writing to a
+                            #terminal even when the codepage is set to cp1251.
+                            #An extra encoding step seems to be needed.
+                            stream.write((fs % msg).encode(stream.encoding))
                     else:
                         stream.write(fs % msg)
                 except UnicodeError: