OpenStack Study: base_handler.py

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# 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

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class BaseHandler(object):

"""Base class to handle loading filter and weight classes."""

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    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)

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    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))

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    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)]