def _get_sitemap_full_url(sitemap_url):
    if not django_apps.is_installed('django.contrib.sites'):
        raise ImproperlyConfigured("ping_google requires django.contrib.sites, which isn't installed.")

    if sitemap_url is None:
        try:
            # First, try to get the "index" sitemap URL.
            sitemap_url = reverse('django.contrib.sitemaps.views.index')
        except NoReverseMatch:
            try:
                # Next, try for the "global" sitemap URL.
                sitemap_url = reverse('django.contrib.sitemaps.views.sitemap')
            except NoReverseMatch:
                pass

    if sitemap_url is None:
        raise SitemapNotFound("You didn't provide a sitemap_url, and the sitemap URL couldn't be auto-detected.")

    Site = django_apps.get_model('sites.Site')
    current_site = Site.objects.get_current()
    return 'http://%s%s' % (current_site.domain, sitemap_url) 

def _get_sitemap_full_url(sitemap_url):
    if not django_apps.is_installed('django.contrib.sites'):
        raise ImproperlyConfigured("ping_google requires django.contrib.sites, which isn't installed.")

    if sitemap_url is None:
        try:
            # First, try to get the "index" sitemap URL.
            sitemap_url = reverse('django.contrib.sitemaps.views.index')
        except NoReverseMatch:
            try:
                # Next, try for the "global" sitemap URL.
                sitemap_url = reverse('django.contrib.sitemaps.views.sitemap')
            except NoReverseMatch:
                pass

    if sitemap_url is None:
        raise SitemapNotFound("You didn't provide a sitemap_url, and the sitemap URL couldn't be auto-detected.")

    Site = django_apps.get_model('sites.Site')
    current_site = Site.objects.get_current()
    return 'http://%s%s' % (current_site.domain, sitemap_url) 

def _get_sitemap_full_url(sitemap_url):
    if not django_apps.is_installed('django.contrib.sites'):
        raise ImproperlyConfigured("ping_google requires django.contrib.sites, which isn't installed.")

    if sitemap_url is None:
        try:
            # First, try to get the "index" sitemap URL.
            sitemap_url = reverse('django.contrib.sitemaps.views.index')
        except NoReverseMatch:
            try:
                # Next, try for the "global" sitemap URL.
                sitemap_url = reverse('django.contrib.sitemaps.views.sitemap')
            except NoReverseMatch:
                pass

    if sitemap_url is None:
        raise SitemapNotFound("You didn't provide a sitemap_url, and the sitemap URL couldn't be auto-detected.")

    Site = django_apps.get_model('sites.Site')
    current_site = Site.objects.get_current()
    return 'http://%s%s' % (current_site.domain, sitemap_url) 

def login(self, **credentials):
        """
        Sets the Factory to appear as if it has successfully logged into a site.

        Returns True if login is possible; False if the provided credentials
        are incorrect, or the user is inactive, or if the sessions framework is
        not available.
        """
        from django.contrib.auth import authenticate
        user = authenticate(**credentials)
        if (user and user.is_active and
                apps.is_installed('django.contrib.sessions')):
            self._login(user)
            return True
        else:
            return False 

def _get_sitemap_full_url(sitemap_url):
    if not django_apps.is_installed('django.contrib.sites'):
        raise ImproperlyConfigured("ping_google requires django.contrib.sites, which isn't installed.")

    if sitemap_url is None:
        try:
            # First, try to get the "index" sitemap URL.
            sitemap_url = reverse('django.contrib.sitemaps.views.index')
        except NoReverseMatch:
            try:
                # Next, try for the "global" sitemap URL.
                sitemap_url = reverse('django.contrib.sitemaps.views.sitemap')
            except NoReverseMatch:
                pass

    if sitemap_url is None:
        raise SitemapNotFound("You didn't provide a sitemap_url, and the sitemap URL couldn't be auto-detected.")

    Site = django_apps.get_model('sites.Site')
    current_site = Site.objects.get_current()
    return 'http://%s%s' % (current_site.domain, sitemap_url) 

def _session(self):
        """
        Obtains the current session variables.
        """
        if apps.is_installed('django.contrib.sessions'):
            engine = import_module(settings.SESSION_ENGINE)
            cookie = self.cookies.get(settings.SESSION_COOKIE_NAME, None)
            if cookie:
                return engine.SessionStore(cookie.value)
            else:
                s = engine.SessionStore()
                s.save()
                self.cookies[settings.SESSION_COOKIE_NAME] = s.session_key
                return s
        return {} 

def login(self, **credentials):
        """
        Sets the Factory to appear as if it has successfully logged into a site.

        Returns True if login is possible; False if the provided credentials
        are incorrect, or the user is inactive, or if the sessions framework is
        not available.
        """
        from django.contrib.auth import authenticate, login
        user = authenticate(**credentials)
        if (user and user.is_active and
                apps.is_installed('django.contrib.sessions')):
            engine = import_module(settings.SESSION_ENGINE)

            # Create a fake request to store login details.
            request = HttpRequest()

            if self.session:
                request.session = self.session
            else:
                request.session = engine.SessionStore()
            login(request, user)

            # Save the session values.
            request.session.save()

            # Set the cookie to represent the session.
            session_cookie = settings.SESSION_COOKIE_NAME
            self.cookies[session_cookie] = request.session.session_key
            cookie_data = {
                'max-age': None,
                'path': '/',
                'domain': settings.SESSION_COOKIE_DOMAIN,
                'secure': settings.SESSION_COOKIE_SECURE or None,
                'expires': None,
            }
            self.cookies[session_cookie].update(cookie_data)

            return True
        else:
            return False 

def __init__(self):
        if not apps.is_installed('django.contrib.sites'):
            raise ImproperlyConfigured(
                "You cannot use RedirectFallbackMiddleware when "
                "django.contrib.sites is not installed."
            ) 

def ping_google(sitemap_url=None, ping_url=PING_URL):
    """
    Alerts Google that the sitemap for the current site has been updated.
    If sitemap_url is provided, it should be an absolute path to the sitemap
    for this site -- e.g., '/sitemap.xml'. If sitemap_url is not provided, this
    function will attempt to deduce it by using urlresolvers.reverse().
    """
    if sitemap_url is None:
        try:
            # First, try to get the "index" sitemap URL.
            sitemap_url = urlresolvers.reverse('django.contrib.sitemaps.views.index')
        except urlresolvers.NoReverseMatch:
            try:
                # Next, try for the "global" sitemap URL.
                sitemap_url = urlresolvers.reverse('django.contrib.sitemaps.views.sitemap')
            except urlresolvers.NoReverseMatch:
                pass

    if sitemap_url is None:
        raise SitemapNotFound("You didn't provide a sitemap_url, and the sitemap URL couldn't be auto-detected.")

    if not django_apps.is_installed('django.contrib.sites'):
        raise ImproperlyConfigured("ping_google requires django.contrib.sites, which isn't installed.")
    Site = django_apps.get_model('sites.Site')
    current_site = Site.objects.get_current()
    url = "http://%s%s" % (current_site.domain, sitemap_url)
    params = urlencode({'sitemap': url})
    urlopen("%s?%s" % (ping_url, params)) 

def get_urls(self, page=1, site=None, protocol=None):
        # Determine protocol
        if self.protocol is not None:
            protocol = self.protocol
        if protocol is None:
            protocol = 'http'

        # Determine domain
        if site is None:
            if django_apps.is_installed('django.contrib.sites'):
                Site = django_apps.get_model('sites.Site')
                try:
                    site = Site.objects.get_current()
                except Site.DoesNotExist:
                    pass
            if site is None:
                raise ImproperlyConfigured(
                    "To use sitemaps, either enable the sites framework or pass "
                    "a Site/RequestSite object in your view."
                )
        domain = site.domain

        if getattr(self, 'i18n', False):
            urls = []
            current_lang_code = translation.get_language()
            for lang_code, lang_name in settings.LANGUAGES:
                translation.activate(lang_code)
                urls += self._urls(page, protocol, domain)
            translation.activate(current_lang_code)
        else:
            urls = self._urls(page, protocol, domain)

        return urls 

def static(path):
    global _static
    if _static is None:
        if apps.is_installed('django.contrib.staticfiles'):
            from django.contrib.staticfiles.templatetags.staticfiles import static as _static
        else:
            from django.templatetags.static import static as _static
    return _static(path) 

def check_dependencies(self):
        """
        Check that all things needed to run the admin have been correctly installed.

        The default implementation checks that admin and contenttypes apps are
        installed, as well as the auth context processor.
        """
        if not apps.is_installed('django.contrib.admin'):
            raise ImproperlyConfigured(
                "Put 'django.contrib.admin' in your INSTALLED_APPS "
                "setting in order to use the admin application.")
        if not apps.is_installed('django.contrib.contenttypes'):
            raise ImproperlyConfigured(
                "Put 'django.contrib.contenttypes' in your INSTALLED_APPS "
                "setting in order to use the admin application.")
        try:
            default_template_engine = Engine.get_default()
        except Exception:
            # Skip this non-critical check:
            # 1. if the user has a non-trivial TEMPLATES setting and Django
            #    can't find a default template engine
            # 2. if anything goes wrong while loading template engines, in
            #    order to avoid raising an exception from a confusing location
            # Catching ImproperlyConfigured suffices for 1. but 2. requires
            # catching all exceptions.
            pass
        else:
            if ('django.contrib.auth.context_processors.auth'
                    not in default_template_engine.context_processors):
                raise ImproperlyConfigured(
                    "Enable 'django.contrib.auth.context_processors.auth' "
                    "in your TEMPLATES setting in order to use the admin "
                    "application.") 

def items(self):
        if not django_apps.is_installed('django.contrib.sites'):
            raise ImproperlyConfigured("FlatPageSitemap requires django.contrib.sites, which isn't installed.")
        Site = django_apps.get_model('sites.Site')
        current_site = Site.objects.get_current()
        return current_site.flatpage_set.filter(registration_required=False) 

def get_current_site(request):
    """
    Checks if contrib.sites is installed and returns either the current
    ``Site`` object or a ``RequestSite`` object based on the request.
    """
    # Imports are inside the function because its point is to avoid importing
    # the Site models when django.contrib.sites isn't installed.
    if apps.is_installed('django.contrib.sites'):
        from .models import Site
        return Site.objects.get_current(request)
    else:
        from .requests import RequestSite
        return RequestSite(request) 

def is_installed(appname):
        return appname in settings.INSTALLED_APPS 

def is_installed(appname):
        return appname in settings.INSTALLED_APPS #or apps.is_installed(appname) 

def handle_simple(cls, path):
        if apps.is_installed('django.contrib.staticfiles'):
            from django.contrib.staticfiles.storage import staticfiles_storage
            return staticfiles_storage.url(path)
        else:
            return urljoin(PrefixNode.handle_simple("STATIC_URL"), quote(path)) 

def __init__(self, get_response=None):
        if not apps.is_installed('django.contrib.sites'):
            raise ImproperlyConfigured(
                "You cannot use RedirectFallbackMiddleware when "
                "django.contrib.sites is not installed."
            )
        super().__init__(get_response) 

def get_urls(self, page=1, site=None, protocol=None):
        # Determine protocol
        if self.protocol is not None:
            protocol = self.protocol
        if protocol is None:
            protocol = 'http'

        # Determine domain
        if site is None:
            if django_apps.is_installed('django.contrib.sites'):
                Site = django_apps.get_model('sites.Site')
                try:
                    site = Site.objects.get_current()
                except Site.DoesNotExist:
                    pass
            if site is None:
                raise ImproperlyConfigured(
                    "To use sitemaps, either enable the sites framework or pass "
                    "a Site/RequestSite object in your view."
                )
        domain = site.domain

        if getattr(self, 'i18n', False):
            urls = []
            current_lang_code = translation.get_language()
            for lang_code, lang_name in settings.LANGUAGES:
                translation.activate(lang_code)
                urls += self._urls(page, protocol, domain)
            translation.activate(current_lang_code)
        else:
            urls = self._urls(page, protocol, domain)

        return urls 

def check_dependencies(**kwargs):
    """
    Check that the admin's dependencies are correctly installed.
    """
    errors = []
    # contrib.contenttypes must be installed.
    if not apps.is_installed('django.contrib.contenttypes'):
        missing_app = checks.Error(
            "'django.contrib.contenttypes' must be in INSTALLED_APPS in order "
            "to use the admin application.",
            id="admin.E401",
        )
        errors.append(missing_app)
    # The auth context processor must be installed if using the default
    # authentication backend.
    try:
        default_template_engine = Engine.get_default()
    except Exception:
        # Skip this non-critical check:
        # 1. if the user has a non-trivial TEMPLATES setting and Django
        #    can't find a default template engine
        # 2. if anything goes wrong while loading template engines, in
        #    order to avoid raising an exception from a confusing location
        # Catching ImproperlyConfigured suffices for 1. but 2. requires
        # catching all exceptions.
        pass
    else:
        if ('django.contrib.auth.context_processors.auth'
                not in default_template_engine.context_processors and
                'django.contrib.auth.backends.ModelBackend' in settings.AUTHENTICATION_BACKENDS):
            missing_template = checks.Error(
                "'django.contrib.auth.context_processors.auth' must be in "
                "TEMPLATES in order to use the admin application.",
                id="admin.E402"
            )
            errors.append(missing_template)
    return errors 

def __init__(self, get_response=None):
        if not apps.is_installed('django.contrib.sites'):
            raise ImproperlyConfigured(
                'You cannot use RedirectFallbackMiddleware when '
                'django.contrib.sites is not installed.'
            )
        super(RedirectFallbackMiddleware, self).__init__(get_response) 

def handle_simple(cls, path):
        if apps.is_installed('django.contrib.staticfiles'):
            from django.contrib.staticfiles.storage import staticfiles_storage
            return staticfiles_storage.url(path)
        else:
            return urljoin(PrefixNode.handle_simple("STATIC_URL"), quote(path)) 

def __init__(self, get_response=None):
        if not apps.is_installed('django.contrib.sites'):
            raise ImproperlyConfigured(
                "You cannot use RedirectFallbackMiddleware when "
                "django.contrib.sites is not installed."
            )
        super().__init__(get_response) 

def get_urls(self, page=1, site=None, protocol=None):
        # Determine protocol
        if self.protocol is not None:
            protocol = self.protocol
        if protocol is None:
            protocol = 'http'

        # Determine domain
        if site is None:
            if django_apps.is_installed('django.contrib.sites'):
                Site = django_apps.get_model('sites.Site')
                try:
                    site = Site.objects.get_current()
                except Site.DoesNotExist:
                    pass
            if site is None:
                raise ImproperlyConfigured(
                    "To use sitemaps, either enable the sites framework or pass "
                    "a Site/RequestSite object in your view."
                )
        domain = site.domain

        if getattr(self, 'i18n', False):
            urls = []
            current_lang_code = translation.get_language()
            for lang_code, lang_name in settings.LANGUAGES:
                translation.activate(lang_code)
                urls += self._urls(page, protocol, domain)
            translation.activate(current_lang_code)
        else:
            urls = self._urls(page, protocol, domain)

        return urls 

def check_dependencies(**kwargs):
    """
    Check that the admin's dependencies are correctly installed.
    """
    errors = []
    # contrib.contenttypes must be installed.
    if not apps.is_installed('django.contrib.contenttypes'):
        missing_app = checks.Error(
            "'django.contrib.contenttypes' must be in INSTALLED_APPS in order "
            "to use the admin application.",
            id="admin.E401",
        )
        errors.append(missing_app)
    # The auth context processor must be installed if using the default
    # authentication backend.
    try:
        default_template_engine = Engine.get_default()
    except Exception:
        # Skip this non-critical check:
        # 1. if the user has a non-trivial TEMPLATES setting and Django
        #    can't find a default template engine
        # 2. if anything goes wrong while loading template engines, in
        #    order to avoid raising an exception from a confusing location
        # Catching ImproperlyConfigured suffices for 1. but 2. requires
        # catching all exceptions.
        pass
    else:
        if ('django.contrib.auth.context_processors.auth'
                not in default_template_engine.context_processors and
                'django.contrib.auth.backends.ModelBackend' in settings.AUTHENTICATION_BACKENDS):
            missing_template = checks.Error(
                "'django.contrib.auth.context_processors.auth' must be in "
                "TEMPLATES in order to use the admin application.",
                id="admin.E402"
            )
            errors.append(missing_template)
    return errors 

def ready(self):
        # Install cache purging signal handlers
        if getattr(settings, 'WAGTAILAPI_USE_FRONTENDCACHE', False):
            if apps.is_installed('wagtail.contrib.frontend_cache'):
                from wagtail.api.v2.signal_handlers import register_signal_handlers
                register_signal_handlers()
            else:
                raise ImproperlyConfigured("The setting 'WAGTAILAPI_USE_FRONTENDCACHE' is True but 'wagtail.contrib.frontend_cache' is not in INSTALLED_APPS.") 

def handle_simple(cls, path):
        if apps.is_installed('django.contrib.staticfiles'):
            from django.contrib.staticfiles.storage import staticfiles_storage
            return staticfiles_storage.url(path)
        else:
            return urljoin(PrefixNode.handle_simple("STATIC_URL"), quote(path)) 

def __init__(self, get_response=None):
        if not apps.is_installed('django.contrib.sites'):
            raise ImproperlyConfigured(
                "You cannot use RedirectFallbackMiddleware when "
                "django.contrib.sites is not installed."
            )
        super(RedirectFallbackMiddleware, self).__init__(get_response) 

def get_urls(self, page=1, site=None, protocol=None):
        # Determine protocol
        if self.protocol is not None:
            protocol = self.protocol
        if protocol is None:
            protocol = 'http'

        # Determine domain
        if site is None:
            if django_apps.is_installed('django.contrib.sites'):
                Site = django_apps.get_model('sites.Site')
                try:
                    site = Site.objects.get_current()
                except Site.DoesNotExist:
                    pass
            if site is None:
                raise ImproperlyConfigured(
                    "To use sitemaps, either enable the sites framework or pass "
                    "a Site/RequestSite object in your view."
                )
        domain = site.domain

        if getattr(self, 'i18n', False):
            urls = []
            current_lang_code = translation.get_language()
            for lang_code, lang_name in settings.LANGUAGES:
                translation.activate(lang_code)
                urls += self._urls(page, protocol, domain)
            translation.activate(current_lang_code)
        else:
            urls = self._urls(page, protocol, domain)

        return urls 

def check_dependencies(**kwargs):
    """
    Check that the admin's dependencies are correctly installed.
    """
    errors = []
    # contrib.contenttypes must be installed.
    if not apps.is_installed('django.contrib.contenttypes'):
        missing_app = checks.Error(
            "'django.contrib.contenttypes' must be in INSTALLED_APPS in order "
            "to use the admin application.",
            id="admin.E401",
        )
        errors.append(missing_app)
    # The auth context processor must be installed if using the default
    # authentication backend.
    try:
        default_template_engine = Engine.get_default()
    except Exception:
        # Skip this non-critical check:
        # 1. if the user has a non-trivial TEMPLATES setting and Django
        #    can't find a default template engine
        # 2. if anything goes wrong while loading template engines, in
        #    order to avoid raising an exception from a confusing location
        # Catching ImproperlyConfigured suffices for 1. but 2. requires
        # catching all exceptions.
        pass
    else:
        if ('django.contrib.auth.context_processors.auth'
                not in default_template_engine.context_processors and
                'django.contrib.auth.backends.ModelBackend' in settings.AUTHENTICATION_BACKENDS):
            missing_template = checks.Error(
                "'django.contrib.auth.context_processors.auth' must be in "
                "TEMPLATES in order to use the admin application.",
                id="admin.E402"
            )
            errors.append(missing_template)
    return errors