Minor
diff --git a/Lib/fontTools/ttLib/tables/otTables.py b/Lib/fontTools/ttLib/tables/otTables.py
index 80b3b08..8720a88 100644
--- a/Lib/fontTools/ttLib/tables/otTables.py
+++ b/Lib/fontTools/ttLib/tables/otTables.py
@@ -160,7 +160,7 @@
mapping = self.mapping = {}
items = list(mapping.items())
getGlyphID = font.getGlyphID
- gidItems = [(getGlyphID(item[0]), getGlyphID(item[1])) for item in items]
+ gidItems = ((getGlyphID(a), getGlyphID(b)) for a,b in items)
sortableItems = sorted(zip(gidItems, items))
# figure out format