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stbi/Lib/site-packages/django/apps/registry.py

+import functools
+import sys
+import threading
+import warnings
+from collections import Counter, defaultdict
+from functools import partial
+
+from django.core.exceptions import AppRegistryNotReady, ImproperlyConfigured
+
+from .config import AppConfig
+
+
+class Apps:
+    """
+    A registry that stores the configuration of installed applications.
+
+    It also keeps track of models, e.g. to provide reverse relations.
+    """
+
+    def __init__(self, installed_apps=()):
+        # installed_apps is set to None when creating the master registry
+        # because it cannot be populated at that point. Other registries must
+        # provide a list of installed apps and are populated immediately.
+        if installed_apps is None and hasattr(sys.modules[__name__], 'apps'):
+            raise RuntimeError("You must supply an installed_apps argument.")
+
+        # Mapping of app labels => model names => model classes. Every time a
+        # model is imported, ModelBase.__new__ calls apps.register_model which
+        # creates an entry in all_models. All imported models are registered,
+        # regardless of whether they're defined in an installed application
+        # and whether the registry has been populated. Since it isn't possible
+        # to reimport a module safely (it could reexecute initialization code)
+        # all_models is never overridden or reset.
+        self.all_models = defaultdict(dict)
+
+        # Mapping of labels to AppConfig instances for installed apps.
+        self.app_configs = {}
+
+        # Stack of app_configs. Used to store the current state in
+        # set_available_apps and set_installed_apps.
+        self.stored_app_configs = []
+
+        # Whether the registry is populated.
+        self.apps_ready = self.models_ready = self.ready = False
+        # For the autoreloader.
+        self.ready_event = threading.Event()
+
+        # Lock for thread-safe population.
+        self._lock = threading.RLock()
+        self.loading = False
+
+        # Maps ("app_label", "modelname") tuples to lists of functions to be
+        # called when the corresponding model is ready. Used by this class's
+        # `lazy_model_operation()` and `do_pending_operations()` methods.
+        self._pending_operations = defaultdict(list)
+
+        # Populate apps and models, unless it's the master registry.
+        if installed_apps is not None:
+            self.populate(installed_apps)
+
+    def populate(self, installed_apps=None):
+        """
+        Load application configurations and models.
+
+        Import each application module and then each model module.
+
+        It is thread-safe and idempotent, but not reentrant.
+        """
+        if self.ready:
+            return
+
+        # populate() might be called by two threads in parallel on servers
+        # that create threads before initializing the WSGI callable.
+        with self._lock:
+            if self.ready:
+                return
+
+            # An RLock prevents other threads from entering this section. The
+            # compare and set operation below is atomic.
+            if self.loading:
+                # Prevent reentrant calls to avoid running AppConfig.ready()
+                # methods twice.
+                raise RuntimeError("populate() isn't reentrant")
+            self.loading = True
+
+            # Phase 1: initialize app configs and import app modules.
+            for entry in installed_apps:
+                if isinstance(entry, AppConfig):
+                    app_config = entry
+                else:
+                    app_config = AppConfig.create(entry)
+                if app_config.label in self.app_configs:
+                    raise ImproperlyConfigured(
+                        "Application labels aren't unique, "
+                        "duplicates: %s" % app_config.label)
+
+                self.app_configs[app_config.label] = app_config
+                app_config.apps = self
+
+            # Check for duplicate app names.
+            counts = Counter(
+                app_config.name for app_config in self.app_configs.values())
+            duplicates = [
+                name for name, count in counts.most_common() if count > 1]
+            if duplicates:
+                raise ImproperlyConfigured(
+                    "Application names aren't unique, "
+                    "duplicates: %s" % ", ".join(duplicates))
+
+            self.apps_ready = True
+
+            # Phase 2: import models modules.
+            for app_config in self.app_configs.values():
+                app_config.import_models()
+
+            self.clear_cache()
+
+            self.models_ready = True
+
+            # Phase 3: run ready() methods of app configs.
+            for app_config in self.get_app_configs():
+                app_config.ready()
+
+            self.ready = True
+            self.ready_event.set()
+
+    def check_apps_ready(self):
+        """Raise an exception if all apps haven't been imported yet."""
+        if not self.apps_ready:
+            from django.conf import settings
+            # If "not ready" is due to unconfigured settings, accessing
+            # INSTALLED_APPS raises a more helpful ImproperlyConfigured
+            # exception.
+            settings.INSTALLED_APPS
+            raise AppRegistryNotReady("Apps aren't loaded yet.")
+
+    def check_models_ready(self):
+        """Raise an exception if all models haven't been imported yet."""
+        if not self.models_ready:
+            raise AppRegistryNotReady("Models aren't loaded yet.")
+
+    def get_app_configs(self):
+        """Import applications and return an iterable of app configs."""
+        self.check_apps_ready()
+        return self.app_configs.values()
+
+    def get_app_config(self, app_label):
+        """
+        Import applications and returns an app config for the given label.
+
+        Raise LookupError if no application exists with this label.
+        """
+        self.check_apps_ready()
+        try:
+            return self.app_configs[app_label]
+        except KeyError:
+            message = "No installed app with label '%s'." % app_label
+            for app_config in self.get_app_configs():
+                if app_config.name == app_label:
+                    message += " Did you mean '%s'?" % app_config.label
+                    break
+            raise LookupError(message)
+
+    # This method is performance-critical at least for Django's test suite.
+    @functools.lru_cache(maxsize=None)
+    def get_models(self, include_auto_created=False, include_swapped=False):
+        """
+        Return a list of all installed models.
+
+        By default, the following models aren't included:
+
+        - auto-created models for many-to-many relations without
+          an explicit intermediate table,
+        - models that have been swapped out.
+
+        Set the corresponding keyword argument to True to include such models.
+        """
+        self.check_models_ready()
+
+        result = []
+        for app_config in self.app_configs.values():
+            result.extend(app_config.get_models(include_auto_created, include_swapped))
+        return result
+
+    def get_model(self, app_label, model_name=None, require_ready=True):
+        """
+        Return the model matching the given app_label and model_name.
+
+        As a shortcut, app_label may be in the form <app_label>.<model_name>.
+
+        model_name is case-insensitive.
+
+        Raise LookupError if no application exists with this label, or no
+        model exists with this name in the application. Raise ValueError if
+        called with a single argument that doesn't contain exactly one dot.
+        """
+        if require_ready:
+            self.check_models_ready()
+        else:
+            self.check_apps_ready()
+
+        if model_name is None:
+            app_label, model_name = app_label.split('.')
+
+        app_config = self.get_app_config(app_label)
+
+        if not require_ready and app_config.models is None:
+            app_config.import_models()
+
+        return app_config.get_model(model_name, require_ready=require_ready)
+
+    def register_model(self, app_label, model):
+        # Since this method is called when models are imported, it cannot
+        # perform imports because of the risk of import loops. It mustn't
+        # call get_app_config().
+        model_name = model._meta.model_name
+        app_models = self.all_models[app_label]
+        if model_name in app_models:
+            if (model.__name__ == app_models[model_name].__name__ and
+                    model.__module__ == app_models[model_name].__module__):
+                warnings.warn(
+                    "Model '%s.%s' was already registered. "
+                    "Reloading models is not advised as it can lead to inconsistencies, "
+                    "most notably with related models." % (app_label, model_name),
+                    RuntimeWarning, stacklevel=2)
+            else:
+                raise RuntimeError(
+                    "Conflicting '%s' models in application '%s': %s and %s." %
+                    (model_name, app_label, app_models[model_name], model))
+        app_models[model_name] = model
+        self.do_pending_operations(model)
+        self.clear_cache()
+
+    def is_installed(self, app_name):
+        """
+        Check whether an application with this name exists in the registry.
+
+        app_name is the full name of the app e.g. 'django.contrib.admin'.
+        """
+        self.check_apps_ready()
+        return any(ac.name == app_name for ac in self.app_configs.values())
+
+    def get_containing_app_config(self, object_name):
+        """
+        Look for an app config containing a given object.
+
+        object_name is the dotted Python path to the object.
+
+        Return the app config for the inner application in case of nesting.
+        Return None if the object isn't in any registered app config.
+        """
+        self.check_apps_ready()
+        candidates = []
+        for app_config in self.app_configs.values():
+            if object_name.startswith(app_config.name):
+                subpath = object_name[len(app_config.name):]
+                if subpath == '' or subpath[0] == '.':
+                    candidates.append(app_config)
+        if candidates:
+            return sorted(candidates, key=lambda ac: -len(ac.name))[0]
+
+    def get_registered_model(self, app_label, model_name):
+        """
+        Similar to get_model(), but doesn't require that an app exists with
+        the given app_label.
+
+        It's safe to call this method at import time, even while the registry
+        is being populated.
+        """
+        model = self.all_models[app_label].get(model_name.lower())
+        if model is None:
+            raise LookupError(
+                "Model '%s.%s' not registered." % (app_label, model_name))
+        return model
+
+    @functools.lru_cache(maxsize=None)
+    def get_swappable_settings_name(self, to_string):
+        """
+        For a given model string (e.g. "auth.User"), return the name of the
+        corresponding settings name if it refers to a swappable model. If the
+        referred model is not swappable, return None.
+
+        This method is decorated with lru_cache because it's performance
+        critical when it comes to migrations. Since the swappable settings don't
+        change after Django has loaded the settings, there is no reason to get
+        the respective settings attribute over and over again.
+        """
+        for model in self.get_models(include_swapped=True):
+            swapped = model._meta.swapped
+            # Is this model swapped out for the model given by to_string?
+            if swapped and swapped == to_string:
+                return model._meta.swappable
+            # Is this model swappable and the one given by to_string?
+            if model._meta.swappable and model._meta.label == to_string:
+                return model._meta.swappable
+        return None
+
+    def set_available_apps(self, available):
+        """
+        Restrict the set of installed apps used by get_app_config[s].
+
+        available must be an iterable of application names.
+
+        set_available_apps() must be balanced with unset_available_apps().
+
+        Primarily used for performance optimization in TransactionTestCase.
+
+        This method is safe in the sense that it doesn't trigger any imports.
+        """
+        available = set(available)
+        installed = {app_config.name for app_config in self.get_app_configs()}
+        if not available.issubset(installed):
+            raise ValueError(
+                "Available apps isn't a subset of installed apps, extra apps: %s"
+                % ", ".join(available - installed)
+            )
+
+        self.stored_app_configs.append(self.app_configs)
+        self.app_configs = {
+            label: app_config
+            for label, app_config in self.app_configs.items()
+            if app_config.name in available
+        }
+        self.clear_cache()
+
+    def unset_available_apps(self):
+        """Cancel a previous call to set_available_apps()."""
+        self.app_configs = self.stored_app_configs.pop()
+        self.clear_cache()
+
+    def set_installed_apps(self, installed):
+        """
+        Enable a different set of installed apps for get_app_config[s].
+
+        installed must be an iterable in the same format as INSTALLED_APPS.
+
+        set_installed_apps() must be balanced with unset_installed_apps(),
+        even if it exits with an exception.
+
+        Primarily used as a receiver of the setting_changed signal in tests.
+
+        This method may trigger new imports, which may add new models to the
+        registry of all imported models. They will stay in the registry even
+        after unset_installed_apps(). Since it isn't possible to replay
+        imports safely (e.g. that could lead to registering listeners twice),
+        models are registered when they're imported and never removed.
+        """
+        if not self.ready:
+            raise AppRegistryNotReady("App registry isn't ready yet.")
+        self.stored_app_configs.append(self.app_configs)
+        self.app_configs = {}
+        self.apps_ready = self.models_ready = self.loading = self.ready = False
+        self.clear_cache()
+        self.populate(installed)
+
+    def unset_installed_apps(self):
+        """Cancel a previous call to set_installed_apps()."""
+        self.app_configs = self.stored_app_configs.pop()
+        self.apps_ready = self.models_ready = self.ready = True
+        self.clear_cache()
+
+    def clear_cache(self):
+        """
+        Clear all internal caches, for methods that alter the app registry.
+
+        This is mostly used in tests.
+        """
+        # Call expire cache on each model. This will purge
+        # the relation tree and the fields cache.
+        self.get_models.cache_clear()
+        if self.ready:
+            # Circumvent self.get_models() to prevent that the cache is refilled.
+            # This particularly prevents that an empty value is cached while cloning.
+            for app_config in self.app_configs.values():
+                for model in app_config.get_models(include_auto_created=True):
+                    model._meta._expire_cache()
+
+    def lazy_model_operation(self, function, *model_keys):
+        """
+        Take a function and a number of ("app_label", "modelname") tuples, and
+        when all the corresponding models have been imported and registered,
+        call the function with the model classes as its arguments.
+
+        The function passed to this method must accept exactly n models as
+        arguments, where n=len(model_keys).
+        """
+        # Base case: no arguments, just execute the function.
+        if not model_keys:
+            function()
+        # Recursive case: take the head of model_keys, wait for the
+        # corresponding model class to be imported and registered, then apply
+        # that argument to the supplied function. Pass the resulting partial
+        # to lazy_model_operation() along with the remaining model args and
+        # repeat until all models are loaded and all arguments are applied.
+        else:
+            next_model, *more_models = model_keys
+
+            # This will be executed after the class corresponding to next_model
+            # has been imported and registered. The `func` attribute provides
+            # duck-type compatibility with partials.
+            def apply_next_model(model):
+                next_function = partial(apply_next_model.func, model)
+                self.lazy_model_operation(next_function, *more_models)
+            apply_next_model.func = function
+
+            # If the model has already been imported and registered, partially
+            # apply it to the function now. If not, add it to the list of
+            # pending operations for the model, where it will be executed with
+            # the model class as its sole argument once the model is ready.
+            try:
+                model_class = self.get_registered_model(*next_model)
+            except LookupError:
+                self._pending_operations[next_model].append(apply_next_model)
+            else:
+                apply_next_model(model_class)
+
+    def do_pending_operations(self, model):
+        """
+        Take a newly-prepared model and pass it to each function waiting for
+        it. This is called at the very end of Apps.register_model().
+        """
+        key = model._meta.app_label, model._meta.model_name
+        for function in self._pending_operations.pop(key, []):
+            function(model)
+
+
+apps = Apps(installed_apps=None)