diff --git a/test/Django-2.1.15/__init__.py b/test/Django-2.1.15/__init__.py
new file mode 100644
index 0000000..3600fbc
--- /dev/null
+++ b/test/Django-2.1.15/__init__.py
@@ -0,0 +1,24 @@
+from django.utils.version import get_version
+
+VERSION = (2, 1, 15, 'final', 0)
+
+__version__ = get_version(VERSION)
+
+
+def setup(set_prefix=True):
+    """
+    Configure the settings (this happens as a side effect of accessing the
+    first setting), configure logging and populate the app registry.
+    Set the thread-local urlresolvers script prefix if `set_prefix` is True.
+    """
+    from django.apps import apps
+    from django.conf import settings
+    from django.urls import set_script_prefix
+    from django.utils.log import configure_logging
+
+    configure_logging(settings.LOGGING_CONFIG, settings.LOGGING)
+    if set_prefix:
+        set_script_prefix(
+            '/' if settings.FORCE_SCRIPT_NAME is None else settings.FORCE_SCRIPT_NAME
+        )
+    apps.populate(settings.INSTALLED_APPS)
diff --git a/test/Django-2.1.15/__main__.py b/test/Django-2.1.15/__main__.py
new file mode 100644
index 0000000..8b96e91
--- /dev/null
+++ b/test/Django-2.1.15/__main__.py
@@ -0,0 +1,9 @@
+"""
+Invokes django-admin when the django module is run as a script.
+
+Example: python -m django check
+"""
+from django.core import management
+
+if __name__ == "__main__":
+    management.execute_from_command_line()
diff --git a/test/Django-2.1.15/config.py b/test/Django-2.1.15/config.py
new file mode 100644
index 0000000..157fda7
--- /dev/null
+++ b/test/Django-2.1.15/config.py
@@ -0,0 +1,203 @@
+import os
+from importlib import import_module
+
+from django.core.exceptions import ImproperlyConfigured
+from django.utils.module_loading import module_has_submodule
+
+MODELS_MODULE_NAME = 'models'
+
+
+class AppConfig:
+    """Class representing a Django application and its configuration."""
+
+    def __init__(self, app_name, app_module):
+        # Full Python path to the application e.g. 'django.contrib.admin'.
+        self.name = app_name
+
+        # Root module for the application e.g. <module 'django.contrib.admin'
+        # from 'django/contrib/admin/__init__.py'>.
+        self.module = app_module
+
+        # Reference to the Apps registry that holds this AppConfig. Set by the
+        # registry when it registers the AppConfig instance.
+        self.apps = None
+
+        # The following attributes could be defined at the class level in a
+        # subclass, hence the test-and-set pattern.
+
+        # Last component of the Python path to the application e.g. 'admin'.
+        # This value must be unique across a Django project.
+        if not hasattr(self, 'label'):
+            self.label = app_name.rpartition(".")[2]
+
+        # Human-readable name for the application e.g. "Admin".
+        if not hasattr(self, 'verbose_name'):
+            self.verbose_name = self.label.title()
+
+        # Filesystem path to the application directory e.g.
+        # '/path/to/django/contrib/admin'.
+        if not hasattr(self, 'path'):
+            self.path = self._path_from_module(app_module)
+
+        # Module containing models e.g. <module 'django.contrib.admin.models'
+        # from 'django/contrib/admin/models.py'>. Set by import_models().
+        # None if the application doesn't have a models module.
+        self.models_module = None
+
+        # Mapping of lower case model names to model classes. Initially set to
+        # None to prevent accidental access before import_models() runs.
+        self.models = None
+
+    def __repr__(self):
+        return '<%s: %s>' % (self.__class__.__name__, self.label)
+
+    def _path_from_module(self, module):
+        """Attempt to determine app's filesystem path from its module."""
+        # See #21874 for extended discussion of the behavior of this method in
+        # various cases.
+        # Convert paths to list because Python's _NamespacePath doesn't support
+        # indexing.
+        paths = list(getattr(module, '__path__', []))
+        if len(paths) != 1:
+            filename = getattr(module, '__file__', None)
+            if filename is not None:
+                paths = [os.path.dirname(filename)]
+            else:
+                # For unknown reasons, sometimes the list returned by __path__
+                # contains duplicates that must be removed (#25246).
+                paths = list(set(paths))
+        if len(paths) > 1:
+            raise ImproperlyConfigured(
+                "The app module %r has multiple filesystem locations (%r); "
+                "you must configure this app with an AppConfig subclass "
+                "with a 'path' class attribute." % (module, paths))
+        elif not paths:
+            raise ImproperlyConfigured(
+                "The app module %r has no filesystem location, "
+                "you must configure this app with an AppConfig subclass "
+                "with a 'path' class attribute." % (module,))
+        return paths[0]
+
+    @classmethod
+    def create(cls, entry):
+        """
+        Factory that creates an app config from an entry in INSTALLED_APPS.
+        """
+        try:
+            # If import_module succeeds, entry is a path to an app module,
+            # which may specify an app config class with default_app_config.
+            # Otherwise, entry is a path to an app config class or an error.
+            module = import_module(entry)
+
+        except ImportError:
+            # Track that importing as an app module failed. If importing as an
+            # app config class fails too, we'll trigger the ImportError again.
+            module = None
+
+            mod_path, _, cls_name = entry.rpartition('.')
+
+            # Raise the original exception when entry cannot be a path to an
+            # app config class.
+            if not mod_path:
+                raise
+
+        else:
+            try:
+                # If this works, the app module specifies an app config class.
+                entry = module.default_app_config
+            except AttributeError:
+                # Otherwise, it simply uses the default app config class.
+                return cls(entry, module)
+            else:
+                mod_path, _, cls_name = entry.rpartition('.')
+
+        # If we're reaching this point, we must attempt to load the app config
+        # class located at <mod_path>.<cls_name>
+        mod = import_module(mod_path)
+        try:
+            cls = getattr(mod, cls_name)
+        except AttributeError:
+            if module is None:
+                # If importing as an app module failed, that error probably
+                # contains the most informative traceback. Trigger it again.
+                import_module(entry)
+            else:
+                raise
+
+        # Check for obvious errors. (This check prevents duck typing, but
+        # it could be removed if it became a problem in practice.)
+        if not issubclass(cls, AppConfig):
+            raise ImproperlyConfigured(
+                "'%s' isn't a subclass of AppConfig." % entry)
+
+        # Obtain app name here rather than in AppClass.__init__ to keep
+        # all error checking for entries in INSTALLED_APPS in one place.
+        try:
+            app_name = cls.name
+        except AttributeError:
+            raise ImproperlyConfigured(
+                "'%s' must supply a name attribute." % entry)
+
+        # Ensure app_name points to a valid module.
+        try:
+            app_module = import_module(app_name)
+        except ImportError:
+            raise ImproperlyConfigured(
+                "Cannot import '%s'. Check that '%s.%s.name' is correct." % (
+                    app_name, mod_path, cls_name,
+                )
+            )
+
+        # Entry is a path to an app config class.
+        return cls(app_name, app_module)
+
+    def get_model(self, model_name, require_ready=True):
+        """
+        Return the model with the given case-insensitive model_name.
+
+        Raise LookupError if no model exists with this name.
+        """
+        if require_ready:
+            self.apps.check_models_ready()
+        else:
+            self.apps.check_apps_ready()
+        try:
+            return self.models[model_name.lower()]
+        except KeyError:
+            raise LookupError(
+                "App '%s' doesn't have a '%s' model." % (self.label, model_name))
+
+    def get_models(self, include_auto_created=False, include_swapped=False):
+        """
+        Return an iterable of 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.
+        Keyword arguments aren't documented; they're a private API.
+        """
+        self.apps.check_models_ready()
+        for model in self.models.values():
+            if model._meta.auto_created and not include_auto_created:
+                continue
+            if model._meta.swapped and not include_swapped:
+                continue
+            yield model
+
+    def import_models(self):
+        # Dictionary of models for this app, primarily maintained in the
+        # 'all_models' attribute of the Apps this AppConfig is attached to.
+        self.models = self.apps.all_models[self.label]
+
+        if module_has_submodule(self.module, MODELS_MODULE_NAME):
+            models_module_name = '%s.%s' % (self.name, MODELS_MODULE_NAME)
+            self.models_module = import_module(models_module_name)
+
+    def ready(self):
+        """
+        Override this method in subclasses to run code when Django starts.
+        """
diff --git a/test/Django-2.1.15/registry.py b/test/Django-2.1.15/registry.py
new file mode 100644
index 0000000..e01352b
--- /dev/null
+++ b/test/Django-2.1.15/registry.py
@@ -0,0 +1,423 @@
+import functools
+import sys
+import threading
+import warnings
+from collections import Counter, OrderedDict, 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(OrderedDict)
+
+        # Mapping of labels to AppConfig instances for installed apps.
+        self.app_configs = OrderedDict()
+
+        # 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
+
+        # 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
+
+    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(list(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 = OrderedDict(
+            (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 = OrderedDict()
+        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[0], model_keys[1:]
+
+            # 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)
diff --git a/test/Django-2.1.15/shortcuts.py b/test/Django-2.1.15/shortcuts.py
new file mode 100644
index 0000000..7ab1df0
--- /dev/null
+++ b/test/Django-2.1.15/shortcuts.py
@@ -0,0 +1,158 @@
+"""
+This module collects helper functions and classes that "span" multiple levels
+of MVC. In other words, these functions/classes introduce controlled coupling
+for convenience's sake.
+"""
+import warnings
+
+from django.http import (
+    Http404, HttpResponse, HttpResponsePermanentRedirect, HttpResponseRedirect,
+)
+from django.template import loader
+from django.urls import NoReverseMatch, reverse
+from django.utils.deprecation import RemovedInDjango30Warning
+from django.utils.functional import Promise
+
+
+def render_to_response(template_name, context=None, content_type=None, status=None, using=None):
+    """
+    Return a HttpResponse whose content is filled with the result of calling
+    django.template.loader.render_to_string() with the passed arguments.
+    """
+    warnings.warn(
+        'render_to_response() is deprecated in favor of render(). It has the '
+        'same signature except that it also requires a request.',
+        RemovedInDjango30Warning, stacklevel=2,
+    )
+    content = loader.render_to_string(template_name, context, using=using)
+    return HttpResponse(content, content_type, status)
+
+
+def render(request, template_name, context=None, content_type=None, status=None, using=None):
+    """
+    Return a HttpResponse whose content is filled with the result of calling
+    django.template.loader.render_to_string() with the passed arguments.
+    """
+    content = loader.render_to_string(template_name, context, request, using=using)
+    return HttpResponse(content, content_type, status)
+
+
+def redirect(to, *args, permanent=False, **kwargs):
+    """
+    Return an HttpResponseRedirect to the appropriate URL for the arguments
+    passed.
+
+    The arguments could be:
+
+        * A model: the model's `get_absolute_url()` function will be called.
+
+        * A view name, possibly with arguments: `urls.reverse()` will be used
+          to reverse-resolve the name.
+
+        * A URL, which will be used as-is for the redirect location.
+
+    Issues a temporary redirect by default; pass permanent=True to issue a
+    permanent redirect.
+    """
+    redirect_class = HttpResponsePermanentRedirect if permanent else HttpResponseRedirect
+    return redirect_class(resolve_url(to, *args, **kwargs))
+
+
+def _get_queryset(klass):
+    """
+    Return a QuerySet or a Manager.
+    Duck typing in action: any class with a `get()` method (for
+    get_object_or_404) or a `filter()` method (for get_list_or_404) might do
+    the job.
+    """
+    # If it is a model class or anything else with ._default_manager
+    if hasattr(klass, '_default_manager'):
+        return klass._default_manager.all()
+    return klass
+
+
+def get_object_or_404(klass, *args, **kwargs):
+    """
+    Use get() to return an object, or raise a Http404 exception if the object
+    does not exist.
+
+    klass may be a Model, Manager, or QuerySet object. All other passed
+    arguments and keyword arguments are used in the get() query.
+
+    Like with QuerySet.get(), MultipleObjectsReturned is raised if more than
+    one object is found.
+    """
+    queryset = _get_queryset(klass)
+    if not hasattr(queryset, 'get'):
+        klass__name = klass.__name__ if isinstance(klass, type) else klass.__class__.__name__
+        raise ValueError(
+            "First argument to get_object_or_404() must be a Model, Manager, "
+            "or QuerySet, not '%s'." % klass__name
+        )
+    try:
+        return queryset.get(*args, **kwargs)
+    except queryset.model.DoesNotExist:
+        raise Http404('No %s matches the given query.' % queryset.model._meta.object_name)
+
+
+def get_list_or_404(klass, *args, **kwargs):
+    """
+    Use filter() to return a list of objects, or raise a Http404 exception if
+    the list is empty.
+
+    klass may be a Model, Manager, or QuerySet object. All other passed
+    arguments and keyword arguments are used in the filter() query.
+    """
+    queryset = _get_queryset(klass)
+    if not hasattr(queryset, 'filter'):
+        klass__name = klass.__name__ if isinstance(klass, type) else klass.__class__.__name__
+        raise ValueError(
+            "First argument to get_list_or_404() must be a Model, Manager, or "
+            "QuerySet, not '%s'." % klass__name
+        )
+    obj_list = list(queryset.filter(*args, **kwargs))
+    if not obj_list:
+        raise Http404('No %s matches the given query.' % queryset.model._meta.object_name)
+    return obj_list
+
+
+def resolve_url(to, *args, **kwargs):
+    """
+    Return a URL appropriate for the arguments passed.
+
+    The arguments could be:
+
+        * A model: the model's `get_absolute_url()` function will be called.
+
+        * A view name, possibly with arguments: `urls.reverse()` will be used
+          to reverse-resolve the name.
+
+        * A URL, which will be returned as-is.
+    """
+    # If it's a model, use get_absolute_url()
+    if hasattr(to, 'get_absolute_url'):
+        return to.get_absolute_url()
+
+    if isinstance(to, Promise):
+        # Expand the lazy instance, as it can cause issues when it is passed
+        # further to some Python functions like urlparse.
+        to = str(to)
+
+    if isinstance(to, str):
+        # Handle relative URLs
+        if to.startswith(('./', '../')):
+            return to
+
+    # Next try a reverse URL resolution.
+    try:
+        return reverse(to, args=args, kwargs=kwargs)
+    except NoReverseMatch:
+        # If this is a callable, re-raise.
+        if callable(to):
+            raise
+        # If this doesn't "feel" like a URL, re-raise.
+        if '/' not in to and '.' not in to:
+            raise
+
+    # Finally, fall back and assume it's a URL
+    return to