Used OrderedDict.fromkeys() to initialize OrderedDict with None values.

django/contrib/admin/options.py

@@ -627,8 +627,8 @@ class ModelAdmin(BaseModelAdmin):
         exclude = exclude or None
 
         # Remove declared form fields which are in readonly_fields.
-        new_attrs = OrderedDict(
-            (f, None) for f in readonly_fields
+        new_attrs = OrderedDict.fromkeys(
+            f for f in readonly_fields
             if f in self.form.declared_fields
         )
         form = type(self.form.__name__, (self.form,), new_attrs)

django/core/management/commands/dumpdata.py

@@ -87,8 +87,8 @@ class Command(BaseCommand):
         if len(app_labels) == 0:
             if primary_keys:
                 raise CommandError("You can only use --pks option with one model")
-            app_list = OrderedDict(
-                (app_config, None) for app_config in apps.get_app_configs()
+            app_list = OrderedDict.fromkeys(
+                app_config for app_config in apps.get_app_configs()
                 if app_config.models_module is not None and app_config not in excluded_apps
             )
         else:

django/utils/datastructures.py

@@ -10,7 +10,7 @@ class OrderedSet:
     """
 
     def __init__(self, iterable=None):
-        self.dict = OrderedDict(((x, None) for x in iterable) if iterable else [])
+        self.dict = OrderedDict.fromkeys(iterable or ())
 
     def add(self, item):
         self.dict[item] = None