(Merge 3.3) _PyUnicode_Writer() now also reuses Unicode singletons:

vstinner · vstinner · commit fb84b5d48d11 · 2013-03-06T19:29:09.000+01:00
empty string and latin1 single character
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
@@ -12821,7 +12821,7 @@ _PyUnicodeWriter_Finish(_PyUnicodeWriter *writer)
         writer->buffer = newbuffer;
     }
     assert(_PyUnicode_CheckConsistency(writer->buffer, 1));
-    return writer->buffer;
+    return unicode_result_ready(writer->buffer);
 }
 
 void

Original file line number	Diff line number	Diff line change
`@@ -12821,7 +12821,7 @@ _PyUnicodeWriter_Finish(_PyUnicodeWriter *writer)`
`12821`	`12821`	`writer->buffer = newbuffer;`
`12822`	`12822`	`}`
`12823`	`12823`	`assert(_PyUnicode_CheckConsistency(writer->buffer, 1));`
`12824`		`- return writer->buffer;`
	`12824`	`+ return unicode_result_ready(writer->buffer);`
`12825`	`12825`	`}`
`12826`	`12826`
`12827`	`12827`	`void`