Change file check from isinstance(value, file) to hasattr(value, 'read') so that file-like objects are handled.

-                if isinstance(value, file):
-                    file_object = value
-                    files.append((name, file_object.name, file_object.read()))
+                if hasattr(value, 'read'):
+                    files.append((name, value.name, value.read()))