160 lines
5.2 KiB
Python
160 lines
5.2 KiB
Python
# vim: tabstop=4 shiftwidth=4 softtabstop=4
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# Copyright 2012 OpenStack Foundation
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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REGISTRY = {}
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_future_dependencies = {}
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_future_optionals = {}
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class UnresolvableDependencyException(Exception):
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def __init__(self, name):
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msg = 'Unregistered dependency: %s' % name
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super(UnresolvableDependencyException, self).__init__(msg)
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def provider(name):
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"""Register the wrapped dependency provider under the specified name."""
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def wrapper(cls):
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def wrapped(init):
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def __wrapped_init__(self, *args, **kwargs):
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"""Initialize the wrapped object and add it to the registry."""
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init(self, *args, **kwargs)
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REGISTRY[name] = self
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resolve_future_dependencies(name)
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return __wrapped_init__
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cls.__init__ = wrapped(cls.__init__)
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return cls
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return wrapper
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def _process_dependencies(obj):
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# Any dependencies that can be resolved immediately are resolved.
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# Dependencies that cannot be resolved immediately are stored for
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# resolution in resolve_future_dependencies.
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def process(obj, attr_name, unresolved_in_out):
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for dependency in getattr(obj, attr_name, []):
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if dependency not in REGISTRY:
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# We don't know about this dependency, so save it for later.
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unresolved_in_out.setdefault(dependency, []).append(obj)
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continue
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setattr(obj, dependency, REGISTRY[dependency])
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process(obj, '_dependencies', _future_dependencies)
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process(obj, '_optionals', _future_optionals)
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def requires(*dependencies):
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"""Inject specified dependencies from the registry into the instance."""
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def wrapper(self, *args, **kwargs):
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"""Inject each dependency from the registry."""
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self.__wrapped_init__(*args, **kwargs)
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_process_dependencies(self)
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def wrapped(cls):
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"""Note the required dependencies on the object for later injection.
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The dependencies of the parent class are combined with that of the
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child class to create a new set of dependencies.
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"""
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existing_dependencies = getattr(cls, '_dependencies', set())
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cls._dependencies = existing_dependencies.union(dependencies)
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if not hasattr(cls, '__wrapped_init__'):
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cls.__wrapped_init__ = cls.__init__
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cls.__init__ = wrapper
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return cls
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return wrapped
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def optional(*dependencies):
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"""Optionally inject specified dependencies from the registry into the
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instance.
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"""
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def wrapper(self, *args, **kwargs):
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"""Inject each dependency from the registry."""
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self.__wrapped_init__(*args, **kwargs)
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_process_dependencies(self)
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def wrapped(cls):
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"""Note the optional dependencies on the object for later injection.
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The dependencies of the parent class are combined with that of the
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child class to create a new set of dependencies.
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"""
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existing_optionals = getattr(cls, '_optionals', set())
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cls._optionals = existing_optionals.union(dependencies)
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if not hasattr(cls, '__wrapped_init__'):
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cls.__wrapped_init__ = cls.__init__
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cls.__init__ = wrapper
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return cls
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return wrapped
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def resolve_future_dependencies(provider_name=None):
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if provider_name:
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# A provider was registered, so take care of any objects depending on
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# it.
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targets = _future_dependencies.pop(provider_name, [])
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targets.extend(_future_optionals.pop(provider_name, []))
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for target in targets:
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setattr(target, provider_name, REGISTRY[provider_name])
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return
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# Resolve optional dependencies, sets the attribute to None if there's no
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# provider registered.
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for dependency, targets in _future_optionals.iteritems():
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provider = REGISTRY.get(dependency)
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for target in targets:
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setattr(target, dependency, provider)
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_future_optionals.clear()
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# Resolve optional dependencies, raises UnresolvableDependencyException if
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# there's no provider registered.
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try:
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for dependency, targets in _future_dependencies.iteritems():
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if dependency not in REGISTRY:
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raise UnresolvableDependencyException(dependency)
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for target in targets:
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setattr(target, dependency, REGISTRY[dependency])
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finally:
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_future_dependencies.clear()
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def reset():
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"""Reset the registry of providers.
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This is useful for unit testing to ensure that tests don't use providers
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from previous tests.
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"""
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REGISTRY.clear()
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_future_dependencies.clear()
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_future_optionals.clear()
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