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417 lines
14 KiB
417 lines
14 KiB
"""Extensible class instrumentation.
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The :mod:`sqlalchemy.ext.instrumentation` package provides for alternate
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systems of class instrumentation within the ORM. Class instrumentation
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refers to how the ORM places attributes on the class which maintain
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data and track changes to that data, as well as event hooks installed
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on the class.
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.. note::
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The extension package is provided for the benefit of integration
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with other object management packages, which already perform
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their own instrumentation. It is not intended for general use.
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For examples of how the instrumentation extension is used,
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see the example :ref:`examples_instrumentation`.
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"""
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import weakref
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from .. import util
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from ..orm import attributes
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from ..orm import base as orm_base
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from ..orm import collections
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from ..orm import exc as orm_exc
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from ..orm import instrumentation as orm_instrumentation
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from ..orm.instrumentation import _default_dict_getter
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from ..orm.instrumentation import _default_manager_getter
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from ..orm.instrumentation import _default_state_getter
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from ..orm.instrumentation import ClassManager
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from ..orm.instrumentation import InstrumentationFactory
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INSTRUMENTATION_MANAGER = "__sa_instrumentation_manager__"
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"""Attribute, elects custom instrumentation when present on a mapped class.
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Allows a class to specify a slightly or wildly different technique for
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tracking changes made to mapped attributes and collections.
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Only one instrumentation implementation is allowed in a given object
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inheritance hierarchy.
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The value of this attribute must be a callable and will be passed a class
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object. The callable must return one of:
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- An instance of an :class:`.InstrumentationManager` or subclass
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- An object implementing all or some of InstrumentationManager (TODO)
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- A dictionary of callables, implementing all or some of the above (TODO)
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- An instance of a :class:`.ClassManager` or subclass
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This attribute is consulted by SQLAlchemy instrumentation
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resolution, once the :mod:`sqlalchemy.ext.instrumentation` module
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has been imported. If custom finders are installed in the global
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instrumentation_finders list, they may or may not choose to honor this
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attribute.
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"""
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def find_native_user_instrumentation_hook(cls):
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"""Find user-specified instrumentation management for a class."""
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return getattr(cls, INSTRUMENTATION_MANAGER, None)
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instrumentation_finders = [find_native_user_instrumentation_hook]
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"""An extensible sequence of callables which return instrumentation
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implementations
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When a class is registered, each callable will be passed a class object.
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If None is returned, the
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next finder in the sequence is consulted. Otherwise the return must be an
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instrumentation factory that follows the same guidelines as
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sqlalchemy.ext.instrumentation.INSTRUMENTATION_MANAGER.
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By default, the only finder is find_native_user_instrumentation_hook, which
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searches for INSTRUMENTATION_MANAGER. If all finders return None, standard
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ClassManager instrumentation is used.
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"""
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class ExtendedInstrumentationRegistry(InstrumentationFactory):
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"""Extends :class:`.InstrumentationFactory` with additional
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bookkeeping, to accommodate multiple types of
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class managers.
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"""
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_manager_finders = weakref.WeakKeyDictionary()
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_state_finders = weakref.WeakKeyDictionary()
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_dict_finders = weakref.WeakKeyDictionary()
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_extended = False
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def _locate_extended_factory(self, class_):
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for finder in instrumentation_finders:
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factory = finder(class_)
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if factory is not None:
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manager = self._extended_class_manager(class_, factory)
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return manager, factory
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else:
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return None, None
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def _check_conflicts(self, class_, factory):
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existing_factories = self._collect_management_factories_for(
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class_
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).difference([factory])
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if existing_factories:
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raise TypeError(
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"multiple instrumentation implementations specified "
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"in %s inheritance hierarchy: %r"
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% (class_.__name__, list(existing_factories))
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)
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def _extended_class_manager(self, class_, factory):
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manager = factory(class_)
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if not isinstance(manager, ClassManager):
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manager = _ClassInstrumentationAdapter(class_, manager)
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if factory != ClassManager and not self._extended:
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# somebody invoked a custom ClassManager.
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# reinstall global "getter" functions with the more
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# expensive ones.
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self._extended = True
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_install_instrumented_lookups()
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self._manager_finders[class_] = manager.manager_getter()
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self._state_finders[class_] = manager.state_getter()
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self._dict_finders[class_] = manager.dict_getter()
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return manager
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def _collect_management_factories_for(self, cls):
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"""Return a collection of factories in play or specified for a
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hierarchy.
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Traverses the entire inheritance graph of a cls and returns a
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collection of instrumentation factories for those classes. Factories
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are extracted from active ClassManagers, if available, otherwise
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instrumentation_finders is consulted.
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"""
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hierarchy = util.class_hierarchy(cls)
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factories = set()
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for member in hierarchy:
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manager = self.manager_of_class(member)
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if manager is not None:
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factories.add(manager.factory)
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else:
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for finder in instrumentation_finders:
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factory = finder(member)
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if factory is not None:
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break
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else:
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factory = None
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factories.add(factory)
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factories.discard(None)
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return factories
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def unregister(self, class_):
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super(ExtendedInstrumentationRegistry, self).unregister(class_)
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if class_ in self._manager_finders:
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del self._manager_finders[class_]
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del self._state_finders[class_]
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del self._dict_finders[class_]
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def manager_of_class(self, cls):
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if cls is None:
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return None
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try:
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finder = self._manager_finders.get(cls, _default_manager_getter)
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except TypeError:
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# due to weakref lookup on invalid object
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return None
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else:
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return finder(cls)
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def state_of(self, instance):
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if instance is None:
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raise AttributeError("None has no persistent state.")
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return self._state_finders.get(
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instance.__class__, _default_state_getter
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)(instance)
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def dict_of(self, instance):
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if instance is None:
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raise AttributeError("None has no persistent state.")
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return self._dict_finders.get(
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instance.__class__, _default_dict_getter
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)(instance)
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orm_instrumentation._instrumentation_factory = (
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_instrumentation_factory
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) = ExtendedInstrumentationRegistry()
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orm_instrumentation.instrumentation_finders = instrumentation_finders
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class InstrumentationManager(object):
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"""User-defined class instrumentation extension.
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:class:`.InstrumentationManager` can be subclassed in order
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to change
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how class instrumentation proceeds. This class exists for
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the purposes of integration with other object management
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frameworks which would like to entirely modify the
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instrumentation methodology of the ORM, and is not intended
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for regular usage. For interception of class instrumentation
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events, see :class:`.InstrumentationEvents`.
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The API for this class should be considered as semi-stable,
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and may change slightly with new releases.
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"""
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# r4361 added a mandatory (cls) constructor to this interface.
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# given that, perhaps class_ should be dropped from all of these
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# signatures.
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def __init__(self, class_):
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pass
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def manage(self, class_, manager):
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setattr(class_, "_default_class_manager", manager)
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def unregister(self, class_, manager):
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delattr(class_, "_default_class_manager")
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def manager_getter(self, class_):
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def get(cls):
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return cls._default_class_manager
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return get
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def instrument_attribute(self, class_, key, inst):
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pass
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def post_configure_attribute(self, class_, key, inst):
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pass
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def install_descriptor(self, class_, key, inst):
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setattr(class_, key, inst)
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def uninstall_descriptor(self, class_, key):
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delattr(class_, key)
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def install_member(self, class_, key, implementation):
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setattr(class_, key, implementation)
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def uninstall_member(self, class_, key):
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delattr(class_, key)
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def instrument_collection_class(self, class_, key, collection_class):
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return collections.prepare_instrumentation(collection_class)
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def get_instance_dict(self, class_, instance):
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return instance.__dict__
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def initialize_instance_dict(self, class_, instance):
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pass
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def install_state(self, class_, instance, state):
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setattr(instance, "_default_state", state)
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def remove_state(self, class_, instance):
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delattr(instance, "_default_state")
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def state_getter(self, class_):
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return lambda instance: getattr(instance, "_default_state")
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def dict_getter(self, class_):
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return lambda inst: self.get_instance_dict(class_, inst)
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class _ClassInstrumentationAdapter(ClassManager):
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"""Adapts a user-defined InstrumentationManager to a ClassManager."""
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def __init__(self, class_, override):
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self._adapted = override
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self._get_state = self._adapted.state_getter(class_)
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self._get_dict = self._adapted.dict_getter(class_)
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ClassManager.__init__(self, class_)
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def manage(self):
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self._adapted.manage(self.class_, self)
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def unregister(self):
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self._adapted.unregister(self.class_, self)
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def manager_getter(self):
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return self._adapted.manager_getter(self.class_)
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def instrument_attribute(self, key, inst, propagated=False):
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ClassManager.instrument_attribute(self, key, inst, propagated)
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if not propagated:
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self._adapted.instrument_attribute(self.class_, key, inst)
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def post_configure_attribute(self, key):
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super(_ClassInstrumentationAdapter, self).post_configure_attribute(key)
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self._adapted.post_configure_attribute(self.class_, key, self[key])
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def install_descriptor(self, key, inst):
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self._adapted.install_descriptor(self.class_, key, inst)
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def uninstall_descriptor(self, key):
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self._adapted.uninstall_descriptor(self.class_, key)
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def install_member(self, key, implementation):
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self._adapted.install_member(self.class_, key, implementation)
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def uninstall_member(self, key):
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self._adapted.uninstall_member(self.class_, key)
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def instrument_collection_class(self, key, collection_class):
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return self._adapted.instrument_collection_class(
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self.class_, key, collection_class
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)
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def initialize_collection(self, key, state, factory):
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delegate = getattr(self._adapted, "initialize_collection", None)
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if delegate:
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return delegate(key, state, factory)
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else:
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return ClassManager.initialize_collection(
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self, key, state, factory
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)
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def new_instance(self, state=None):
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instance = self.class_.__new__(self.class_)
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self.setup_instance(instance, state)
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return instance
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def _new_state_if_none(self, instance):
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"""Install a default InstanceState if none is present.
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A private convenience method used by the __init__ decorator.
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"""
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if self.has_state(instance):
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return False
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else:
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return self.setup_instance(instance)
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def setup_instance(self, instance, state=None):
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self._adapted.initialize_instance_dict(self.class_, instance)
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if state is None:
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state = self._state_constructor(instance, self)
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# the given instance is assumed to have no state
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self._adapted.install_state(self.class_, instance, state)
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return state
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def teardown_instance(self, instance):
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self._adapted.remove_state(self.class_, instance)
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def has_state(self, instance):
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try:
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self._get_state(instance)
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except orm_exc.NO_STATE:
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return False
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else:
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return True
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def state_getter(self):
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return self._get_state
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def dict_getter(self):
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return self._get_dict
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def _install_instrumented_lookups():
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"""Replace global class/object management functions
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with ExtendedInstrumentationRegistry implementations, which
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allow multiple types of class managers to be present,
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at the cost of performance.
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This function is called only by ExtendedInstrumentationRegistry
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and unit tests specific to this behavior.
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The _reinstall_default_lookups() function can be called
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after this one to re-establish the default functions.
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"""
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_install_lookups(
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dict(
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instance_state=_instrumentation_factory.state_of,
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instance_dict=_instrumentation_factory.dict_of,
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manager_of_class=_instrumentation_factory.manager_of_class,
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)
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)
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def _reinstall_default_lookups():
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"""Restore simplified lookups."""
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_install_lookups(
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dict(
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instance_state=_default_state_getter,
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instance_dict=_default_dict_getter,
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manager_of_class=_default_manager_getter,
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)
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)
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_instrumentation_factory._extended = False
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def _install_lookups(lookups):
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global instance_state, instance_dict, manager_of_class
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instance_state = lookups["instance_state"]
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instance_dict = lookups["instance_dict"]
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manager_of_class = lookups["manager_of_class"]
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orm_base.instance_state = (
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attributes.instance_state
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) = orm_instrumentation.instance_state = instance_state
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orm_base.instance_dict = (
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attributes.instance_dict
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) = orm_instrumentation.instance_dict = instance_dict
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orm_base.manager_of_class = (
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attributes.manager_of_class
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) = orm_instrumentation.manager_of_class = manager_of_class
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