Index: logging/__init__.py
===================================================================
--- logging/__init__.py	(revision 75042)
+++ logging/__init__.py	(working copy)
@@ -766,28 +766,23 @@
         try:
             msg = self.format(record)
             stream = self.stream
-            fs = "%s\n"
-            if not hasattr(types, "UnicodeType"): #if no unicode support...
-                stream.write(fs % msg)
-            else:
-                try:
-                    if (isinstance(msg, unicode) and
-                        getattr(stream, 'encoding', None)):
-                        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:
-                    stream.write(fs % msg.encode("UTF-8"))
+            try:
+                stream.write(msg + '\n')
+            except UnicodeError:
+                if isinstance(msg, unicode):
+                    # 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.
+                    encoding = getattr(stream, 'encoding', 'ascii')
+                    stream.write(msg.encode(encoding, 'backslashreplace') + '\n')
+                else:
+                    # When stream is codecs.writer object and msg is encoded by
+                    # encoding that isn't stream.encoding, write() raises
+                    # UnicodeDecodeError.
+                    stream.write(msg.encode('string_escape') + '\n')
             self.flush()
         except (KeyboardInterrupt, SystemExit):
             raise
Index: test/test_logging.py
===================================================================
--- test/test_logging.py	(revision 75042)
+++ test/test_logging.py	(working copy)
@@ -887,10 +887,14 @@
             if os.path.isfile(fn):
                 os.remove(fn)
 
+    unicode_message = u'\u0434\u043e \u0441\u0432\u0438\u0434\u0430\u043d\u0438\u044f'
+    escaped_message = '\\u0434\\u043e \\u0441\\u0432\\u0438\\u0434'\
+                      '\\u0430\\u043d\\u0438\\u044f\n'
+
     def test_encoding_cyrillic_unicode(self):
         log = logging.getLogger("test")
         #Get a message in Unicode: Do svidanya in Cyrillic (meaning goodbye)
-        message = u'\u0434\u043e \u0441\u0432\u0438\u0434\u0430\u043d\u0438\u044f'
+        message = self.unicode_message
         #Ensure it's written in a Cyrillic encoding
         writer_class = codecs.getwriter('cp1251')
         writer_class.encoding = 'cp1251'
@@ -908,7 +912,64 @@
         #Compare against what the data should be when encoded in CP-1251
         self.assertEqual(s, '\xe4\xee \xf1\xe2\xe8\xe4\xe0\xed\xe8\xff\n')
 
+    def test_unicode_without_encoding(self):
+        log = logging.getLogger("test")
+        message = self.unicode_message
+        stream = cStringIO.StringIO()
+        handler = logging.StreamHandler(stream)
+        log.addHandler(handler)
+        try:
+            log.warning(message)
+        finally:
+            log.removeHandler(handler)
+            handler.close()
+        s = stream.getvalue()
+        # message should be encoded in utf-8 (fallback encoding).
+        self.assertEqual(s, self.escaped_message)
 
+    def test_unicode_encodeerror_fallback(self):
+        log = logging.getLogger("test")
+        #Get a message in Unicode: Do svidanya in Cyrillic (meaning goodbye)
+        message = self.unicode_message
+
+        writer_class = codecs.getwriter('latin-1')
+        writer_class.encoding = 'latin-1'
+        stream = cStringIO.StringIO()
+        writer = writer_class(stream, 'strict')
+        handler = logging.StreamHandler(writer)
+        log.addHandler(handler)
+        try:
+            log.warning(message)
+        finally:
+            log.removeHandler(handler)
+            handler.close()
+        # check we wrote exactly those bytes, ignoring trailing \n etc
+        s = stream.getvalue()
+        # message should be encoded in ascii with backslash escape.
+        self.assertEqual(s, self.escaped_message)
+
+    def test_encoding_mismatch(self):
+        log = logging.getLogger("test")
+        #Get a message in Unicode: Do svidanya in Cyrillic (meaning goodbye)
+        message = self.unicode_message.encode('utf-8')
+
+        writer_class = codecs.getwriter('latin-1')
+        writer_class.encoding = 'latin-1'
+        stream = cStringIO.StringIO()
+        writer = writer_class(stream, 'strict')
+        handler = logging.StreamHandler(writer)
+        log.addHandler(handler)
+        try:
+            log.warning(message)
+        finally:
+            log.removeHandler(handler)
+            handler.close()
+        # check we wrote exactly those bytes, ignoring trailing \n etc
+        s = stream.getvalue()
+        # message should be encoded in ascii with backslash escape.
+        self.assertEqual(s, message.encode('string_escape') + '\n')
+
+
 # Set the locale to the platform-dependent default.  I have no idea
 # why the test does this, but in any case we save the current locale
 # first and restore it at the end.