Used more augmented assignment statements.

Identified using the following command:

$ git grep -I '\(\<[_a-zA-Z0-9]\+\>\) *= *\1 *[-+/*^%&|<>@]'

django/forms/forms.py

@@ -492,7 +492,7 @@ class BaseForm(RenderableFormMixin):
         """Return all media required to render the widgets on this form."""
         media = Media()
         for field in self.fields.values():
-            media = media + field.widget.media
+            media += field.widget.media
         return media
 
     def is_multipart(self):

django/forms/models.py

@@ -316,7 +316,7 @@ class ModelFormMetaclass(DeclarativeFieldsMetaclass):
             missing_fields = none_model_fields.difference(new_class.declared_fields)
             if missing_fields:
                 message = "Unknown field(s) (%s) specified for %s"
-                message = message % (", ".join(missing_fields), opts.model.__name__)
+                message %= (", ".join(missing_fields), opts.model.__name__)
                 raise FieldError(message)
             # Override default model fields with any custom declared ones
             # (plus, include all the other declared fields).

django/forms/widgets.py

@@ -207,7 +207,7 @@ def media_property(cls):
                 else:
                     m = Media()
                     for medium in extend:
-                        m = m + base[medium]
+                        m += base[medium]
                 return m + Media(definition)
             return Media(definition)
         return base
@@ -945,7 +945,7 @@ class MultiWidget(Widget):
         """
         media = Media()
         for w in self.widgets:
-            media = media + w.media
+            media += w.media
         return media
 
     media = property(_get_media)