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# vim: tabstop=4 shiftwidth=4 softtabstop=4
# Copyright 2012 OpenStack LLC
#
# 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.
REGISTRY = {}
_future_dependencies = {}
class UnresolvableDependencyException(Exception):
def __init__(self, name):
msg = 'Unregistered dependency: %s' % name
super(UnresolvableDependencyException, self).__init__(msg)
def provider(name):
"""Register the wrapped dependency provider under the specified name."""
def wrapper(cls):
def wrapped(init):
def __wrapped_init__(self, *args, **kwargs):
"""Initialize the wrapped object and add it to the registry."""
init(self, *args, **kwargs)
REGISTRY[name] = self
resolve_future_dependencies(name)
return __wrapped_init__
cls.__init__ = wrapped(cls.__init__)
return cls
return wrapper
def requires(*dependencies):
"""Inject specified dependencies from the registry into the instance."""
def wrapper(self, *args, **kwargs):
"""Inject each dependency from the registry."""
self.__wrapped_init__(*args, **kwargs)
for dependency in self._dependencies:
if dependency not in REGISTRY:
if dependency in _future_dependencies:
_future_dependencies[dependency] += [self]
else:
_future_dependencies[dependency] = [self]
continue
setattr(self, dependency, REGISTRY[dependency])
def wrapped(cls):
"""Note the required dependencies on the object for later injection.
The dependencies of the parent class are combined with that of the
child class to create a new set of dependencies.
"""
existing_dependencies = getattr(cls, '_dependencies', set())
cls._dependencies = existing_dependencies.union(dependencies)
if not hasattr(cls, '__wrapped_init__'):
cls.__wrapped_init__ = cls.__init__
cls.__init__ = wrapper
return cls
return wrapped
def resolve_future_dependencies(provider_name=None):
if provider_name:
targets = _future_dependencies.pop(provider_name, [])
for target in targets:
setattr(target, provider_name, REGISTRY[provider_name])
return
try:
for dependency, targets in _future_dependencies.iteritems():
if dependency not in REGISTRY:
raise UnresolvableDependencyException(dependency)
for target in targets:
setattr(target, dependency, REGISTRY[dependency])
finally:
_future_dependencies.clear()
def reset():
"""Reset the registry of providers.
This is useful for unit testing to ensure that tests don't use providers
from previous tests.
"""
REGISTRY.clear()
_future_dependencies.clear()
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