Fixed sorting of dict.keys() generator.
diff --git a/lib3/yaml/emitter.py b/lib3/yaml/emitter.py
index 5c99d2f..8947d04 100644
--- a/lib3/yaml/emitter.py
+++ b/lib3/yaml/emitter.py
@@ -579,8 +579,7 @@
             return tag
         handle = None
         suffix = tag
-        prefixes = self.tag_prefixes.keys()
-        prefixes.sort()
+        prefixes = sorted(self.tag_prefixes.keys())
         for prefix in prefixes:
             if tag.startswith(prefix)   \
                     and (prefix == '!' or len(prefix) < len(tag)):