save LazyLoadingDict in case we do want it later

common/lib/xmodule/lazy_dict.py

+from collections import MutableMapping
+
+class LazyLoadingDict(MutableMapping):
+    """
+    A dictionary object that lazily loads its contents from a provided
+    function on reads (of members that haven't already been set).
+    """
+
+    def __init__(self, loader):
+        '''
+        On the first read from this dictionary, it will call loader() to
+        populate its contents.  loader() must return something dict-like. Any
+        elements set before the first read will be preserved.
+        '''
+        self._contents = {}
+        self._loaded = False
+        self._loader = loader
+        self._deleted = set()
+
+    def __getitem__(self, name):
+        if not (self._loaded or name in self._contents or name in self._deleted):
+            self.load()
+
+        return self._contents[name]
+
+    def __setitem__(self, name, value):
+        self._contents[name] = value
+        self._deleted.discard(name)
+
+    def __delitem__(self, name):
+        del self._contents[name]
+        self._deleted.add(name)
+
+    def __contains__(self, name):
+        self.load()
+        return name in self._contents
+
+    def __len__(self):
+        self.load()
+        return len(self._contents)
+
+    def __iter__(self):
+        self.load()
+        return iter(self._contents)
+
+    def __repr__(self):
+        self.load()
+        return repr(self._contents)
+
+    def load(self):
+        if self._loaded:
+            return
+
+        loaded_contents = self._loader()
+        loaded_contents.update(self._contents)
+        self._contents = loaded_contents
+        self._loaded = True
+

common/lib/xmodule/xmodule/xml_module.py

@@ -11,66 +11,6 @@ import os
 
 log = logging.getLogger(__name__)
 
-# # TODO (cpennington): This was implemented in an attempt to improve performance,
-# # but the actual improvement wasn't measured (and it was implemented late at night).
-# # We should check if it hurts, and whether there's a better way of doing lazy loading
-
-# class LazyLoadingDict(MutableMapping):
-#     """
-#     A dictionary object that lazily loads its contents from a provided
-#     function on reads (of members that haven't already been set).
-#     """
-
-#     def __init__(self, loader):
-#         '''
-#         On the first read from this dictionary, it will call loader() to
-#         populate its contents.  loader() must return something dict-like. Any
-#         elements set before the first read will be preserved.
-#         '''
-#         self._contents = {}
-#         self._loaded = False
-#         self._loader = loader
-#         self._deleted = set()
-
-#     def __getitem__(self, name):
-#         if not (self._loaded or name in self._contents or name in self._deleted):
-#             self.load()
-
-#         return self._contents[name]
-
-#     def __setitem__(self, name, value):
-#         self._contents[name] = value
-#         self._deleted.discard(name)
-
-#     def __delitem__(self, name):
-#         del self._contents[name]
-#         self._deleted.add(name)
-
-#     def __contains__(self, name):
-#         self.load()
-#         return name in self._contents
-
-#     def __len__(self):
-#         self.load()
-#         return len(self._contents)
-
-#     def __iter__(self):
-#         self.load()
-#         return iter(self._contents)
-
-#     def __repr__(self):
-#         self.load()
-#         return repr(self._contents)
-
-#     def load(self):
-#         if self._loaded:
-#             return
-
-#         loaded_contents = self._loader()
-#         loaded_contents.update(self._contents)
-#         self._contents = loaded_contents
-#         self._loaded = True
-
 
 _AttrMapBase = namedtuple('_AttrMap', 'metadata_key to_metadata from_metadata')