Fixed #16833 -- Removed undocumented mixin parameter from the Storage.open() method as this was an undocumented and obscure feature. Thanks to Marty and Russell for sanity-checking.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16824 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/releases/1.4.txt

@@ -527,6 +527,30 @@ This functionality has been removed due to intractable performance and
 security issues. Any existing usage of ``verify_exists`` should be
 removed.
 
+``django.core.files.storage.Storage.open``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``open`` method of the base Storage class took an obscure parameter
+``mixin`` which allowed to dynamically change the base classes of the
+returned file object. In the rare case you relied on the `mixin` parameter,
+you can easily achieve the same by overriding the `open` method, e.g.::
+
+    from django.core.files import File
+    from django.core.files.storage import FileSystemStorage
+
+    class Spam(File):
+        """
+        Spam, spam, spam, spam and spam.
+        """
+        def ham(self):
+            return 'eggs'
+
+    class SpamStorage(FileSystemStorage):
+        """
+        A custom file storage backend.
+        """
+        def open(self, name, mode='rb'):
+            return Spam(open(self.path(name), mode))
 
 .. _deprecated-features-1.4: