Break out common functionality for filters and weights

In the context of openstack.common.scheduler:

base_filter.BaseFilterManager and base_weight.BaseWeightManager had
duplicated code.

This patch breaks that code out into a shared base class:
base_handler.BaseHandler

Change-Id: Ie5232c6dd9876a75170beda71adde90fc6bb4153

3 files changed, 50 insertions, 41 deletions

diff --git a/openstack/common/scheduler/base_filter.py b/openstack/common/scheduler/base_filter.py
index 52c18af..5f2fc9c 100644
--- a/openstack/common/scheduler/base_filter.py
+++ b/openstack/common/scheduler/base_filter.py
@@ -17,9 +17,7 @@
 Filter support
 """
 
-import inspect
-
-from stevedore import extension
+from openstack.common.scheduler import base_handler
 
 
 class BaseFilter(object):
@@ -42,27 +40,11 @@ class BaseFilter(object):
                 yield obj
 
 
-class BaseFilterHandler(object):
+class BaseFilterHandler(base_handler.BaseHandler):
     """ Base class to handle loading filter classes.
 
     This class should be subclassed where one needs to use filters.
     """
-    def __init__(self, filter_class_type, filter_namespace):
-        self.namespace = filter_namespace
-        self.filter_class_type = filter_class_type
-        self.filter_manager = extension.ExtensionManager(filter_namespace)
-
-    def _is_correct_class(self, obj):
-        """Return whether an object is a class of the correct type and
-        is not prefixed with an underscore.
-        """
-        return (inspect.isclass(obj) and
-                not obj.__name__.startswith('_') and
-                issubclass(obj, self.filter_class_type))
-
-    def get_all_classes(self):
-        return [x.plugin for x in self.filter_manager
-                if self._is_correct_class(x.plugin)]
 
     def get_filtered_objects(self, filter_classes, objs,
                              filter_properties):
diff --git a/openstack/common/scheduler/base_handler.py b/openstack/common/scheduler/base_handler.py
new file mode 100644
index 0000000..147d90d
--- /dev/null
+++ b/openstack/common/scheduler/base_handler.py
@@ -0,0 +1,46 @@
+# Copyright (c) 2011-2013 OpenStack Foundation.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+"""
+A common base for handling extension classes.
+
+Used by BaseFilterHandler and BaseWeightHandler
+"""
+
+import inspect
+
+from stevedore import extension
+
+
+class BaseHandler(object):
+    """ Base class to handle loading filter and weight classes.
+    """
+    def __init__(self, modifier_class_type, modifier_namespace):
+        self.namespace = modifier_namespace
+        self.modifier_class_type = modifier_class_type
+        self.extension_manager = extension.ExtensionManager(modifier_namespace)
+
+    def _is_correct_class(self, cls):
+        """Return whether an object is a class of the correct type and
+        is not prefixed with an underscore.
+        """
+        return (inspect.isclass(cls) and
+                not cls.__name__.startswith('_') and
+                issubclass(cls, self.modifier_class_type))
+
+    def get_all_classes(self):
+        # We use a set, as some classes may have an entrypoint of their own,
+        # and also be returned by a function such as 'all_filters' for example
+        return [ext.plugin for ext in self.extension_manager if
+                self._is_correct_class(ext.plugin)]
diff --git a/openstack/common/scheduler/base_weight.py b/openstack/common/scheduler/base_weight.py
index 82f1d25..362685e 100644
--- a/openstack/common/scheduler/base_weight.py
+++ b/openstack/common/scheduler/base_weight.py
@@ -17,9 +17,7 @@
 Pluggable Weighing support
 """
 
-import inspect
-
-from stevedore import extension
+from openstack.common.scheduler import base_handler
 
 
 class WeighedObject(object):
@@ -56,26 +54,9 @@ class BaseWeigher(object):
                            self._weigh_object(obj.obj, weight_properties))
 
 
-class BaseWeightHandler(object):
+class BaseWeightHandler(base_handler.BaseHandler):
     object_class = WeighedObject
 
-    def __init__(self, weighed_object_type, weight_namespace):
-        self.namespace = weight_namespace
-        self.weighed_object_type = weighed_object_type
-        self.weight_manager = extension.ExtensionManager(weight_namespace)
-
-    def _is_correct_class(self, obj):
-        """Return whether an object is a class of the correct type and
-        is not prefixed with an underscore.
-        """
-        return (inspect.isclass(obj) and
-                not obj.__name__.startswith('_') and
-                issubclass(obj, self.weighed_object_type))
-
-    def get_all_classes(self):
-        return [x.plugin for x in self.weight_manager
-                if self._is_correct_class(x.plugin)]
-
     def get_weighed_objects(self, weigher_classes, obj_list,
                             weighing_properties):
         """Return a sorted (highest score first) list of WeighedObjects."""