/Windows/Python3.8/WPy64-3830/WPy64-3830/python-3.8.3.amd64/Lib/site-packages/sqlalchemy/ext/instrumentation.py

"""Extensible class instrumentation.



The :mod:`sqlalchemy.ext.instrumentation` package provides for alternate

systems of class instrumentation within the ORM.  Class instrumentation

refers to how the ORM places attributes on the class which maintain

data and track changes to that data, as well as event hooks installed

on the class.



.. note::

    The extension package is provided for the benefit of integration

    with other object management packages, which already perform

    their own instrumentation.  It is not intended for general use.



For examples of how the instrumentation extension is used,

see the example :ref:`examples_instrumentation`.



"""

import weakref



from .. import util

from ..orm import attributes

from ..orm import base as orm_base

from ..orm import collections

from ..orm import exc as orm_exc

from ..orm import instrumentation as orm_instrumentation

from ..orm.instrumentation import _default_dict_getter

from ..orm.instrumentation import _default_manager_getter

from ..orm.instrumentation import _default_state_getter

from ..orm.instrumentation import ClassManager

from ..orm.instrumentation import InstrumentationFactory





INSTRUMENTATION_MANAGER = "__sa_instrumentation_manager__"

"""Attribute, elects custom instrumentation when present on a mapped class.



Allows a class to specify a slightly or wildly different technique for

tracking changes made to mapped attributes and collections.



Only one instrumentation implementation is allowed in a given object

inheritance hierarchy.



The value of this attribute must be a callable and will be passed a class

object.  The callable must return one of:



  - An instance of an InstrumentationManager or subclass

  - An object implementing all or some of InstrumentationManager (TODO)

  - A dictionary of callables, implementing all or some of the above (TODO)

  - An instance of a ClassManager or subclass



This attribute is consulted by SQLAlchemy instrumentation

resolution, once the :mod:`sqlalchemy.ext.instrumentation` module

has been imported.  If custom finders are installed in the global

instrumentation_finders list, they may or may not choose to honor this

attribute.



"""





def find_native_user_instrumentation_hook(cls):

    """Find user-specified instrumentation management for a class."""

    return getattr(cls, INSTRUMENTATION_MANAGER, None)





instrumentation_finders = [find_native_user_instrumentation_hook]

"""An extensible sequence of callables which return instrumentation

implementations



When a class is registered, each callable will be passed a class object.

If None is returned, the

next finder in the sequence is consulted.  Otherwise the return must be an

instrumentation factory that follows the same guidelines as

sqlalchemy.ext.instrumentation.INSTRUMENTATION_MANAGER.



By default, the only finder is find_native_user_instrumentation_hook, which

searches for INSTRUMENTATION_MANAGER.  If all finders return None, standard

ClassManager instrumentation is used.



"""





class ExtendedInstrumentationRegistry(InstrumentationFactory):

    """Extends :class:`.InstrumentationFactory` with additional

    bookkeeping, to accommodate multiple types of

    class managers.



    """



    _manager_finders = weakref.WeakKeyDictionary()

    _state_finders = weakref.WeakKeyDictionary()

    _dict_finders = weakref.WeakKeyDictionary()

    _extended = False



    def _locate_extended_factory(self, class_):

        for finder in instrumentation_finders:

            factory = finder(class_)

            if factory is not None:

                manager = self._extended_class_manager(class_, factory)

                return manager, factory

        else:

            return None, None



    def _check_conflicts(self, class_, factory):

        existing_factories = self._collect_management_factories_for(

            class_

        ).difference([factory])

        if existing_factories:

            raise TypeError(

                "multiple instrumentation implementations specified "

                "in %s inheritance hierarchy: %r"

                % (class_.__name__, list(existing_factories))

            )



    def _extended_class_manager(self, class_, factory):

        manager = factory(class_)

        if not isinstance(manager, ClassManager):

            manager = _ClassInstrumentationAdapter(class_, manager)



        if factory != ClassManager and not self._extended:

            # somebody invoked a custom ClassManager.

            # reinstall global "getter" functions with the more

            # expensive ones.

            self._extended = True

            _install_instrumented_lookups()



        self._manager_finders[class_] = manager.manager_getter()

        self._state_finders[class_] = manager.state_getter()

        self._dict_finders[class_] = manager.dict_getter()

        return manager



    def _collect_management_factories_for(self, cls):

        """Return a collection of factories in play or specified for a

        hierarchy.



        Traverses the entire inheritance graph of a cls and returns a

        collection of instrumentation factories for those classes. Factories

        are extracted from active ClassManagers, if available, otherwise

        instrumentation_finders is consulted.



        """

        hierarchy = util.class_hierarchy(cls)

        factories = set()

        for member in hierarchy:

            manager = self.manager_of_class(member)

            if manager is not None:

                factories.add(manager.factory)

            else:

                for finder in instrumentation_finders:

                    factory = finder(member)

                    if factory is not None:

                        break

                else:

                    factory = None

                factories.add(factory)

        factories.discard(None)

        return factories



    def unregister(self, class_):

        if class_ in self._manager_finders:

            del self._manager_finders[class_]

            del self._state_finders[class_]

            del self._dict_finders[class_]

        super(ExtendedInstrumentationRegistry, self).unregister(class_)



    def manager_of_class(self, cls):

        if cls is None:

            return None

        try:

            finder = self._manager_finders.get(cls, _default_manager_getter)

        except TypeError:

            # due to weakref lookup on invalid object

            return None

        else:

            return finder(cls)



    def state_of(self, instance):

        if instance is None:

            raise AttributeError("None has no persistent state.")

        return self._state_finders.get(

            instance.__class__, _default_state_getter

        )(instance)



    def dict_of(self, instance):

        if instance is None:

            raise AttributeError("None has no persistent state.")

        return self._dict_finders.get(

            instance.__class__, _default_dict_getter

        )(instance)





orm_instrumentation._instrumentation_factory = (

    _instrumentation_factory

) = ExtendedInstrumentationRegistry()

orm_instrumentation.instrumentation_finders = instrumentation_finders





class InstrumentationManager(object):

    """User-defined class instrumentation extension.



    :class:`.InstrumentationManager` can be subclassed in order

    to change

    how class instrumentation proceeds. This class exists for

    the purposes of integration with other object management

    frameworks which would like to entirely modify the

    instrumentation methodology of the ORM, and is not intended

    for regular usage.  For interception of class instrumentation

    events, see :class:`.InstrumentationEvents`.



    The API for this class should be considered as semi-stable,

    and may change slightly with new releases.



    """



    # r4361 added a mandatory (cls) constructor to this interface.

    # given that, perhaps class_ should be dropped from all of these

    # signatures.



    def __init__(self, class_):

        pass



    def manage(self, class_, manager):

        setattr(class_, "_default_class_manager", manager)



    def dispose(self, class_, manager):

        delattr(class_, "_default_class_manager")



    def manager_getter(self, class_):

        def get(cls):

            return cls._default_class_manager



        return get



    def instrument_attribute(self, class_, key, inst):

        pass



    def post_configure_attribute(self, class_, key, inst):

        pass



    def install_descriptor(self, class_, key, inst):

        setattr(class_, key, inst)



    def uninstall_descriptor(self, class_, key):

        delattr(class_, key)



    def install_member(self, class_, key, implementation):

        setattr(class_, key, implementation)



    def uninstall_member(self, class_, key):

        delattr(class_, key)



    def instrument_collection_class(self, class_, key, collection_class):

        return collections.prepare_instrumentation(collection_class)



    def get_instance_dict(self, class_, instance):

        return instance.__dict__



    def initialize_instance_dict(self, class_, instance):

        pass



    def install_state(self, class_, instance, state):

        setattr(instance, "_default_state", state)



    def remove_state(self, class_, instance):

        delattr(instance, "_default_state")



    def state_getter(self, class_):

        return lambda instance: getattr(instance, "_default_state")



    def dict_getter(self, class_):

        return lambda inst: self.get_instance_dict(class_, inst)





class _ClassInstrumentationAdapter(ClassManager):

    """Adapts a user-defined InstrumentationManager to a ClassManager."""



    def __init__(self, class_, override):

        self._adapted = override

        self._get_state = self._adapted.state_getter(class_)

        self._get_dict = self._adapted.dict_getter(class_)



        ClassManager.__init__(self, class_)



    def manage(self):

        self._adapted.manage(self.class_, self)



    def dispose(self):

        self._adapted.dispose(self.class_)



    def manager_getter(self):

        return self._adapted.manager_getter(self.class_)



    def instrument_attribute(self, key, inst, propagated=False):

        ClassManager.instrument_attribute(self, key, inst, propagated)

        if not propagated:

            self._adapted.instrument_attribute(self.class_, key, inst)



    def post_configure_attribute(self, key):

        super(_ClassInstrumentationAdapter, self).post_configure_attribute(key)

        self._adapted.post_configure_attribute(self.class_, key, self[key])



    def install_descriptor(self, key, inst):

        self._adapted.install_descriptor(self.class_, key, inst)



    def uninstall_descriptor(self, key):

        self._adapted.uninstall_descriptor(self.class_, key)



    def install_member(self, key, implementation):

        self._adapted.install_member(self.class_, key, implementation)



    def uninstall_member(self, key):

        self._adapted.uninstall_member(self.class_, key)



    def instrument_collection_class(self, key, collection_class):

        return self._adapted.instrument_collection_class(

            self.class_, key, collection_class

        )



    def initialize_collection(self, key, state, factory):

        delegate = getattr(self._adapted, "initialize_collection", None)

        if delegate:

            return delegate(key, state, factory)

        else:

            return ClassManager.initialize_collection(

                self, key, state, factory

            )



    def new_instance(self, state=None):

        instance = self.class_.__new__(self.class_)

        self.setup_instance(instance, state)

        return instance



    def _new_state_if_none(self, instance):

        """Install a default InstanceState if none is present.



        A private convenience method used by the __init__ decorator.

        """

        if self.has_state(instance):

            return False

        else:

            return self.setup_instance(instance)



    def setup_instance(self, instance, state=None):

        self._adapted.initialize_instance_dict(self.class_, instance)



        if state is None:

            state = self._state_constructor(instance, self)



        # the given instance is assumed to have no state

        self._adapted.install_state(self.class_, instance, state)

        return state



    def teardown_instance(self, instance):

        self._adapted.remove_state(self.class_, instance)



    def has_state(self, instance):

        try:

            self._get_state(instance)

        except orm_exc.NO_STATE:

            return False

        else:

            return True



    def state_getter(self):

        return self._get_state



    def dict_getter(self):

        return self._get_dict





def _install_instrumented_lookups():

    """Replace global class/object management functions

    with ExtendedInstrumentationRegistry implementations, which

    allow multiple types of class managers to be present,

    at the cost of performance.



    This function is called only by ExtendedInstrumentationRegistry

    and unit tests specific to this behavior.



    The _reinstall_default_lookups() function can be called

    after this one to re-establish the default functions.



    """

    _install_lookups(

        dict(

            instance_state=_instrumentation_factory.state_of,

            instance_dict=_instrumentation_factory.dict_of,

            manager_of_class=_instrumentation_factory.manager_of_class,

        )

    )





def _reinstall_default_lookups():

    """Restore simplified lookups."""

    _install_lookups(

        dict(

            instance_state=_default_state_getter,

            instance_dict=_default_dict_getter,

            manager_of_class=_default_manager_getter,

        )

    )

    _instrumentation_factory._extended = False





def _install_lookups(lookups):

    global instance_state, instance_dict, manager_of_class

    instance_state = lookups["instance_state"]

    instance_dict = lookups["instance_dict"]

    manager_of_class = lookups["manager_of_class"]

    orm_base.instance_state = (

        attributes.instance_state

    ) = orm_instrumentation.instance_state = instance_state

    orm_base.instance_dict = (

        attributes.instance_dict

    ) = orm_instrumentation.instance_dict = instance_dict

    orm_base.manager_of_class = (

        attributes.manager_of_class

    ) = orm_instrumentation.manager_of_class = manager_of_class