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# Copyright (c) 2011-2012 OpenStack, LLC.
# 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.
"""
Pluggable Weighing support
"""
import inspect
from stevedore import extension
class WeighedObject(object):
"""Object with weight information."""
def __init__(self, obj, weight):
self.obj = obj
self.weight = weight
def __repr__(self):
return "<WeighedObject '%s': %s>" % (self.obj, self.weight)
class BaseWeigher(object):
"""Base class for pluggable weighers."""
def _weight_multiplier(self):
"""How weighted this weigher should be. Normally this would
be overriden in a subclass based on a config value.
"""
return 1.0
def _weigh_object(self, obj, weight_properties):
"""Override in a subclass to specify a weight for a specific
object.
"""
return 0.0
def weigh_objects(self, weighed_obj_list, weight_properties):
"""Weigh multiple objects. Override in a subclass if you need
need access to all objects in order to manipulate weights.
"""
constant = self._weight_multiplier()
for obj in weighed_obj_list:
obj.weight += (constant *
self._weigh_object(obj.obj, weight_properties))
class BaseWeightHandler(object):
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."""
if not obj_list:
return []
weighed_objs = [self.object_class(obj, 0.0) for obj in obj_list]
for weigher_cls in weigher_classes:
weigher = weigher_cls()
weigher.weigh_objects(weighed_objs, weighing_properties)
return sorted(weighed_objs, key=lambda x: x.weight, reverse=True)
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