Specify __all__ in mixins and generics

This fixes #2 by specifically saying what will be imported from
`mixins.py` and `generics.py` when a star import is done on these
files.  This is done within `__init__.py`, so the classes can be
imported directly from there.  This prevents an issue where
`rest_framework.mixins` was being imported from `generics.py`, so
users were not able to import `rest_bulk_create.mixins`.

README.rst

@@ -135,5 +135,5 @@ Credits
 
 Current maintainers:
 
-* Miroslav Shubernetskiy - `GitHub <https://github.com/miki725>`_.
-
+* Miroslav Shubernetskiy - `GitHub <https://github.com/miki725>`_
+* Kevin Brown - `GitHub <https://github.com/kevin-brown>`_

rest_framework_bulk/generics.py

@@ -4,6 +4,11 @@
 from . import mixins as bulk_mixins
 
 
+__all__ = ["BulkCreateAPIView", "BulkUpdateAPIView", "BulkDestroyAPIView", "ListBulkCreateAPIView",
+           "ListCreateBulkUpdateAPIView", "ListCreateBulkUpdateDestroyAPIView", "ListBulkCreateUpdateAPIView",
+           "ListBulkCreateUpdateDestroyAPIView"]
+
+
 ##########################################################
 ### Concrete view classes that provide method handlers ###
 ### by composing the mixin classes with the base view. ###

rest_framework_bulk/mixins.py

@@ -5,6 +5,9 @@
 from rest_framework.response import Response
 
 
+__all__ = ["BulkCreateModelMixin", "BulkUpdateModelMixin", "BulkDestroyModelMixin"]
+
+
 class BulkCreateModelMixin(CreateModelMixin):
     """
     Either create a single or many model instances in bulk by using the