Fixed #23832 -- Added timezone aware Storage API.

New Storage.get_{accessed,created,modified}_time() methods convert the
naive time from now-deprecated {accessed,created_modified}_time()
methods into aware objects in UTC if USE_TZ=True.

django/contrib/staticfiles/management/commands/collectstatic.py

@@ -237,15 +237,14 @@ class Command(BaseCommand):
         if self.storage.exists(prefixed_path):
             try:
                 # When was the target file modified last time?
-                target_last_modified = \
+                target_last_modified = self.storage.get_modified_time(prefixed_path)
-                    self.storage.modified_time(prefixed_path)
             except (OSError, NotImplementedError, AttributeError):
-                # The storage doesn't support ``modified_time`` or failed
+                # The storage doesn't support get_modified_time() or failed
                 pass
             else:
                 try:
                     # When was the source file modified last time?
-                    source_last_modified = source_storage.modified_time(path)
+                    source_last_modified = source_storage.get_modified_time(path)
                 except (OSError, NotImplementedError, AttributeError):
                     pass
                 else:

django/core/files/storage.py

@@ -1,5 +1,6 @@
 import errno
 import os
+import warnings
 from datetime import datetime
 
 from django.conf import settings
@@ -7,9 +8,11 @@ from django.core.exceptions import SuspiciousFileOperation
 from django.core.files import File, locks
 from django.core.files.move import file_move_safe
 from django.core.signals import setting_changed
+from django.utils import timezone
 from django.utils._os import abspathu, safe_join
 from django.utils.crypto import get_random_string
 from django.utils.deconstruct import deconstructible
+from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.encoding import filepath_to_uri, force_text
 from django.utils.functional import LazyObject, cached_property
 from django.utils.module_loading import import_string
@@ -140,24 +143,101 @@ class Storage(object):
     def accessed_time(self, name):
         """
         Returns the last accessed time (as datetime object) of the file
-        specified by name.
+        specified by name. Deprecated: use get_accessed_time() instead.
         """
+        warnings.warn(
+            'Storage.accessed_time() is deprecated in favor of get_accessed_time().',
+            RemovedInDjango20Warning,
+            stacklevel=2,
+        )
         raise NotImplementedError('subclasses of Storage must provide an accessed_time() method')
 
     def created_time(self, name):
         """
         Returns the creation time (as datetime object) of the file
-        specified by name.
+        specified by name. Deprecated: use get_created_time() instead.
         """
+        warnings.warn(
+            'Storage.created_time() is deprecated in favor of get_created_time().',
+            RemovedInDjango20Warning,
+            stacklevel=2,
+        )
         raise NotImplementedError('subclasses of Storage must provide a created_time() method')
 
     def modified_time(self, name):
         """
         Returns the last modified time (as datetime object) of the file
-        specified by name.
+        specified by name. Deprecated: use get_modified_time() instead.
         """
+        warnings.warn(
+            'Storage.modified_time() is deprecated in favor of get_modified_time().',
+            RemovedInDjango20Warning,
+            stacklevel=2,
+        )
         raise NotImplementedError('subclasses of Storage must provide a modified_time() method')
 
+    def get_accessed_time(self, name):
+        """
+        Return the last accessed time (as a datetime) of the file specified by
+        name. The datetime will be timezone-aware if USE_TZ=True.
+        """
+        # At the end of the deprecation:
+        # raise NotImplementedError('subclasses of Storage must provide a get_accessed_time() method')
+        warnings.warn(
+            'Storage.accessed_time() is deprecated. '
+            'Storage backends should implement get_accessed_time().',
+            RemovedInDjango20Warning,
+            stacklevel=2,
+        )
+        dt = self.accessed_time(name)
+        return _possibly_make_aware(dt)
+
+    def get_created_time(self, name):
+        """
+        Return the creation time (as a datetime) of the file specified by name.
+        The datetime will be timezone-aware if USE_TZ=True.
+        """
+        # At the end of the deprecation:
+        # raise NotImplementedError('subclasses of Storage must provide a get_created_time() method')
+        warnings.warn(
+            'Storage.created_time() is deprecated. '
+            'Storage backends should implement get_created_time().',
+            RemovedInDjango20Warning,
+            stacklevel=2,
+        )
+        dt = self.created_time(name)
+        return _possibly_make_aware(dt)
+
+    def get_modified_time(self, name):
+        """
+        Return the last modified time (as a datetime) of the file specified by
+        name. The datetime will be timezone-aware if USE_TZ=True.
+        """
+        # At the end of the deprecation:
+        # raise NotImplementedError('subclasses of Storage must provide a get_modified_time() method')
+        warnings.warn(
+            'Storage.modified_time() is deprecated. '
+            'Storage backends should implement get_modified_time().',
+            RemovedInDjango20Warning,
+            stacklevel=2,
+        )
+        dt = self.modified_time(name)
+        return _possibly_make_aware(dt)
+
+
+def _possibly_make_aware(dt):
+    """
+    Convert a datetime object in the local timezone to aware
+    in UTC, if USE_TZ is True.
+    """
+    # This function is only needed to help with the deprecations above and can
+    # be removed in Django 2.0, RemovedInDjango20Warning.
+    if settings.USE_TZ:
+        tz = timezone.get_default_timezone()
+        return timezone.make_aware(dt, tz).astimezone(timezone.utc)
+    else:
+        return dt
+
 
 @deconstructible
 class FileSystemStorage(Storage):
@@ -328,14 +408,52 @@ class FileSystemStorage(Storage):
         return urljoin(self.base_url, filepath_to_uri(name))
 
     def accessed_time(self, name):
+        warnings.warn(
+            'FileSystemStorage.accessed_time() is deprecated in favor of '
+            'get_accessed_time().',
+            RemovedInDjango20Warning,
+            stacklevel=2,
+        )
         return datetime.fromtimestamp(os.path.getatime(self.path(name)))
 
     def created_time(self, name):
+        warnings.warn(
+            'FileSystemStorage.created_time() is deprecated in favor of '
+            'get_created_time().',
+            RemovedInDjango20Warning,
+            stacklevel=2,
+        )
         return datetime.fromtimestamp(os.path.getctime(self.path(name)))
 
     def modified_time(self, name):
+        warnings.warn(
+            'FileSystemStorage.modified_time() is deprecated in favor of '
+            'get_modified_time().',
+            RemovedInDjango20Warning,
+            stacklevel=2,
+        )
         return datetime.fromtimestamp(os.path.getmtime(self.path(name)))
 
+    def _datetime_from_timestamp(self, ts):
+        """
+        If timezone support is enabled, make an aware datetime object in UTC;
+        otherwise make a naive one in the local timezone.
+        """
+        if settings.USE_TZ:
+            # Safe to use .replace() because UTC doesn't have DST
+            return datetime.utcfromtimestamp(ts).replace(tzinfo=timezone.utc)
+        else:
+            return datetime.fromtimestamp(ts)
+
+    def get_accessed_time(self, name):
+        return self._datetime_from_timestamp(os.path.getatime(self.path(name)))
+
+    def get_created_time(self, name):
+        return self._datetime_from_timestamp(os.path.getctime(self.path(name)))
+
+    def get_modified_time(self, name):
+        return self._datetime_from_timestamp(os.path.getmtime(self.path(name)))
+
 
 def get_storage_class(import_path=None):
     return import_string(import_path or settings.DEFAULT_FILE_STORAGE)

docs/internals/deprecation.txt

@@ -135,6 +135,9 @@ details on these changes.
 
 * Support for the template ``Context.has_key()`` method will be removed.
 
+* Support for the ``django.core.files.storage.Storage.accessed_time()``,
+  ``created_time()``, and ``modified_time()`` methods will be removed.
+
 .. _deprecation-removed-in-1.10:
 
 1.10

docs/ref/files/storage.txt

@@ -73,10 +73,9 @@ The ``Storage`` class
     as necessary.
 
     .. note::
-        For methods returning naive ``datetime`` objects, the
+        When methods return naive ``datetime`` objects, the effective timezone
-        effective timezone used will be the current value of
+        used will be the current value of ``os.environ['TZ']``; note that this
-        ``os.environ['TZ']``; note that this is usually set from
+        is usually set from Django's :setting:`TIME_ZONE`.
-        Django's :setting:`TIME_ZONE`.
 
     .. method:: accessed_time(name)
 
@@ -85,6 +84,10 @@ The ``Storage`` class
         able to return the last accessed time this will raise
         ``NotImplementedError`` instead.
 
+        .. deprecated:: 1.10
+
+            Use :meth:`get_accessed_time` instead.
+
     .. method:: created_time(name)
 
         Returns a naive ``datetime`` object containing the creation
@@ -92,6 +95,10 @@ The ``Storage`` class
         return the creation time this will raise
         ``NotImplementedError`` instead.
 
+        .. deprecated:: 1.10
+
+            Use :meth:`get_created_time` instead.
+
     .. method:: delete(name)
 
         Deletes the file referenced by ``name``. If deletion is not supported
@@ -104,6 +111,17 @@ The ``Storage`` class
         in the storage system, or ``False`` if the name is available for a new
         file.
 
+    .. method:: get_accessed_time(name)
+
+        .. versionadded:: 1.10
+
+        Returns a :class:`~datetime.datetime` of the last accessed time of the
+        file. For storage systems unable to return the last accessed time this
+        will raise :exc:`NotImplementedError`.
+
+        If :setting:`USE_TZ` is ``True``, returns an aware ``datetime``,
+        otherwise returns a naive ``datetime`` in the local timezone.
+
     .. method:: get_available_name(name, max_length=None)
 
         Returns a filename based on the ``name`` parameter that's free and
@@ -119,6 +137,28 @@ The ``Storage`` class
         7 character alphanumeric string is appended to the filename before
         the extension.
 
+    .. method:: get_created_time(name)
+
+        .. versionadded:: 1.10
+
+        Returns a :class:`~datetime.datetime` of the creation time of the file.
+        For storage systems unable to return the creation time this will raise
+        :exc:`NotImplementedError`.
+
+        If :setting:`USE_TZ` is ``True``, returns an aware ``datetime``,
+        otherwise returns a naive ``datetime`` in the local timezone.
+
+    .. method:: get_modified_time(name)
+
+        .. versionadded:: 1.10
+
+        Returns a :class:`~datetime.datetime` of the last modified time of the
+        file. For storage systems unable to return the last modified time this
+        will raise :exc:`NotImplementedError`.
+
+        If :setting:`USE_TZ` is ``True``, returns an aware ``datetime``,
+        otherwise returns a naive ``datetime`` in the local timezone.
+
     .. method:: get_valid_name(name)
 
         Returns a filename based on the ``name`` parameter that's suitable
@@ -138,6 +178,10 @@ The ``Storage`` class
         the last modified time, this will raise
         ``NotImplementedError`` instead.
 
+        .. deprecated:: 1.10
+
+            Use :meth:`get_modified_time` instead.
+
     .. method:: open(name, mode='rb')
 
         Opens the file given by ``name``. Note that although the returned file

docs/releases/1.10.txt

@@ -203,7 +203,13 @@ Email
 File Storage
 ~~~~~~~~~~~~
 
-* ...
+* Storage backends now present a timezone-aware API with new methods
+  :meth:`~django.core.files.storage.Storage.get_accessed_time`,
+  :meth:`~django.core.files.storage.Storage.get_created_time`, and
+  :meth:`~django.core.files.storage.Storage.get_modified_time`. They return a
+  timezone-aware ``datetime`` if :setting:`USE_TZ` is ``True`` and a naive
+  ``datetime`` in the local timezone otherwise.
+
 
 File Uploads
 ~~~~~~~~~~~~
@@ -623,6 +629,21 @@ added in Django 1.9::
 
 This prevents confusion about an assignment resulting in an implicit save.
 
+Non-timezone-aware :class:`~django.core.files.storage.Storage` API
+------------------------------------------------------------------
+
+The old, non-timezone-aware methods ``accessed_time()``, ``created_time()``,
+and ``modified_time()`` are deprecated in favor of the new ``get_*_time()``
+methods.
+
+Third-party storage backends should implement the new methods and mark the old
+ones as deprecated. Until then, the new ``get_*_time()`` methods on the base
+:class:`~django.core.files.storage.Storage` class convert ``datetime``\s from
+the old methods as required and emit a deprecation warning as they do so.
+
+Third-party storage backends may retain the old methods as long as they
+wish to support earlier versions of Django.
+
 :mod:`django.contrib.gis`
 -------------------------
 

tests/file_storage/tests.py

@@ -20,14 +20,23 @@ from django.core.files.uploadedfile import (
 )
 from django.db.models.fields.files import FileDescriptor
 from django.test import (
-    LiveServerTestCase, SimpleTestCase, TestCase, override_settings,
+    LiveServerTestCase, SimpleTestCase, TestCase, ignore_warnings,
+    override_settings,
 )
-from django.utils import six
+from django.test.utils import requires_tz_support
+from django.utils import six, timezone
 from django.utils._os import upath
+from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.six.moves.urllib.request import urlopen
 
 from .models import Storage, temp_storage, temp_storage_location
 
+try:
+    import pytz
+except ImportError:
+    pytz = None
+
+
 FILE_SUFFIX_REGEX = '[A-Za-z0-9]{7}'
 
 
@@ -83,7 +92,13 @@ class FileStorageDeconstructionTests(unittest.TestCase):
         self.assertEqual(kwargs, kwargs_orig)
 
 
-class FileStorageTests(SimpleTestCase):
+# Tests for TZ-aware time methods need pytz.
+requires_pytz = unittest.skipIf(pytz is None, "this test requires pytz")
+
+
+class FileStorageTests(TestCase):
+    # Changing TIME_ZONE may issue a query to set the database's timezone,
+    # hence TestCase.
     storage_class = FileSystemStorage
 
     def setUp(self):
@@ -123,7 +138,86 @@ class FileStorageTests(SimpleTestCase):
         self.storage.delete('storage_test')
         self.assertFalse(self.storage.exists('storage_test'))
 
-    def test_file_accessed_time(self):
+    def _test_file_time_getter(self, getter):
+        # Check for correct behavior under both USE_TZ=True and USE_TZ=False.
+        # The tests are similar since they both set up a situation where the
+        # system time zone, Django's TIME_ZONE, and UTC are distinct.
+        self._test_file_time_getter_tz_handling_on(getter)
+        self._test_file_time_getter_tz_handling_off(getter)
+
+    @override_settings(USE_TZ=True, TIME_ZONE='Africa/Algiers')
+    def _test_file_time_getter_tz_handling_on(self, getter):
+        # Django's TZ (and hence the system TZ) is set to Africa/Algiers which
+        # is UTC+1 and has no DST change. We can set the Django TZ to something
+        # else so that UTC, Django's TIME_ZONE, and the system timezone are all
+        # different.
+        now_in_algiers = timezone.make_aware(datetime.now())
+
+        # Use a fixed offset timezone so we don't need pytz.
+        with timezone.override(timezone.get_fixed_timezone(-300)):
+            # At this point the system TZ is +1 and the Django TZ
+            # is -5. The following will be aware in UTC.
+            now = timezone.now()
+            self.assertFalse(self.storage.exists('test.file.tz.on'))
+
+            f = ContentFile('custom contents')
+            f_name = self.storage.save('test.file.tz.on', f)
+            self.addCleanup(self.storage.delete, f_name)
+            dt = getter(f_name)
+            # dt should be aware, in UTC
+            self.assertTrue(timezone.is_aware(dt))
+            self.assertEqual(now.tzname(), dt.tzname())
+
+            # Check that the three timezones are indeed distinct.
+            naive_now = datetime.now()
+            algiers_offset = now_in_algiers.tzinfo.utcoffset(naive_now)
+            django_offset = timezone.get_current_timezone().utcoffset(naive_now)
+            utc_offset = timezone.utc.utcoffset(naive_now)
+            self.assertGreater(algiers_offset, utc_offset)
+            self.assertLess(django_offset, utc_offset)
+
+            # dt and now should be the same effective time.
+            self.assertLess(abs(dt - now), timedelta(seconds=2))
+
+    @override_settings(USE_TZ=False, TIME_ZONE='Africa/Algiers')
+    def _test_file_time_getter_tz_handling_off(self, getter):
+        # Django's TZ (and hence the system TZ) is set to Africa/Algiers which
+        # is UTC+1 and has no DST change. We can set the Django TZ to something
+        # else so that UTC, Django's TIME_ZONE, and the system timezone are all
+        # different.
+        now_in_algiers = timezone.make_aware(datetime.now())
+
+        # Use a fixed offset timezone so we don't need pytz.
+        with timezone.override(timezone.get_fixed_timezone(-300)):
+            # At this point the system TZ is +1 and the Django TZ
+            # is -5.
+            self.assertFalse(self.storage.exists('test.file.tz.off'))
+
+            f = ContentFile('custom contents')
+            f_name = self.storage.save('test.file.tz.off', f)
+            self.addCleanup(self.storage.delete, f_name)
+            dt = getter(f_name)
+            # dt should be naive, in system (+1) TZ
+            self.assertTrue(timezone.is_naive(dt))
+
+            # Check that the three timezones are indeed distinct.
+            naive_now = datetime.now()
+            algiers_offset = now_in_algiers.tzinfo.utcoffset(naive_now)
+            django_offset = timezone.get_current_timezone().utcoffset(naive_now)
+            utc_offset = timezone.utc.utcoffset(naive_now)
+            self.assertGreater(algiers_offset, utc_offset)
+            self.assertLess(django_offset, utc_offset)
+
+            # dt and naive_now should be the same effective time.
+            self.assertLess(abs(dt - naive_now), timedelta(seconds=2))
+            # If we convert dt to an aware object using the Algiers
+            # timezone then it should be the same effective time to
+            # now_in_algiers.
+            _dt = timezone.make_aware(dt, now_in_algiers.tzinfo)
+            self.assertLess(abs(_dt - now_in_algiers), timedelta(seconds=2))
+
+    @requires_pytz
+    def test_file_get_accessed_time(self):
         """
         File storage returns a Datetime object for the last accessed time of
         a file.
@@ -132,47 +226,102 @@ class FileStorageTests(SimpleTestCase):
 
         f = ContentFile('custom contents')
         f_name = self.storage.save('test.file', f)
+        self.addCleanup(self.storage.delete, f_name)
+        atime = self.storage.get_accessed_time(f_name)
+
+        self.assertEqual(atime, datetime.fromtimestamp(os.path.getatime(self.storage.path(f_name))))
+        self.assertLess(timezone.now() - self.storage.get_accessed_time(f_name), timedelta(seconds=2))
+
+    @requires_pytz
+    @requires_tz_support
+    def test_file_get_accessed_time_timezone(self):
+        self._test_file_time_getter(self.storage.get_accessed_time)
+
+    @ignore_warnings(category=RemovedInDjango20Warning)
+    def test_file_accessed_time(self):
+        """
+        File storage returns a datetime for the last accessed time of a file.
+        """
+        self.assertFalse(self.storage.exists('test.file'))
+
+        f = ContentFile('custom contents')
+        f_name = self.storage.save('test.file', f)
+        self.addCleanup(self.storage.delete, f_name)
         atime = self.storage.accessed_time(f_name)
 
-        self.assertEqual(atime, datetime.fromtimestamp(
+        self.assertEqual(atime, datetime.fromtimestamp(os.path.getatime(self.storage.path(f_name))))
-            os.path.getatime(self.storage.path(f_name))))
         self.assertLess(datetime.now() - self.storage.accessed_time(f_name), timedelta(seconds=2))
-        self.storage.delete(f_name)
 
+    @requires_pytz
+    def test_file_get_created_time(self):
+        """
+        File storage returns a datetime for the creation time of a file.
+        """
+        self.assertFalse(self.storage.exists('test.file'))
+
+        f = ContentFile('custom contents')
+        f_name = self.storage.save('test.file', f)
+        self.addCleanup(self.storage.delete, f_name)
+        ctime = self.storage.get_created_time(f_name)
+
+        self.assertEqual(ctime, datetime.fromtimestamp(os.path.getctime(self.storage.path(f_name))))
+        self.assertLess(timezone.now() - self.storage.get_created_time(f_name), timedelta(seconds=2))
+
+    @requires_pytz
+    @requires_tz_support
+    def test_file_get_created_time_timezone(self):
+        self._test_file_time_getter(self.storage.get_created_time)
+
+    @ignore_warnings(category=RemovedInDjango20Warning)
     def test_file_created_time(self):
         """
-        File storage returns a Datetime object for the creation time of
+        File storage returns a datetime for the creation time of a file.
-        a file.
         """
         self.assertFalse(self.storage.exists('test.file'))
 
         f = ContentFile('custom contents')
         f_name = self.storage.save('test.file', f)
         ctime = self.storage.created_time(f_name)
+        self.addCleanup(self.storage.delete, f_name)
 
-        self.assertEqual(ctime, datetime.fromtimestamp(
+        self.assertEqual(ctime, datetime.fromtimestamp(os.path.getctime(self.storage.path(f_name))))
-            os.path.getctime(self.storage.path(f_name))))
         self.assertLess(datetime.now() - self.storage.created_time(f_name), timedelta(seconds=2))
 
-        self.storage.delete(f_name)
+    @requires_pytz
-
+    def test_file_get_modified_time(self):
-    def test_file_modified_time(self):
         """
-        File storage returns a Datetime object for the last modified time of
+        File storage returns a datetime for the last modified time of a file.
-        a file.
         """
         self.assertFalse(self.storage.exists('test.file'))
 
         f = ContentFile('custom contents')
         f_name = self.storage.save('test.file', f)
+        self.addCleanup(self.storage.delete, f_name)
+        mtime = self.storage.get_modified_time(f_name)
+
+        self.assertEqual(mtime, datetime.fromtimestamp(os.path.getmtime(self.storage.path(f_name))))
+        self.assertLess(timezone.now() - self.storage.get_modified_time(f_name), timedelta(seconds=2))
+
+    @requires_pytz
+    @requires_tz_support
+    def test_file_get_modified_time_timezone(self):
+        self._test_file_time_getter(self.storage.get_modified_time)
+
+    @ignore_warnings(category=RemovedInDjango20Warning)
+    def test_file_modified_time(self):
+        """
+        File storage returns a datetime for the last modified time of a file.
+        """
+        self.assertFalse(self.storage.exists('test.file'))
+
+        f = ContentFile('custom contents')
+        f_name = self.storage.save('test.file', f)
+        self.addCleanup(self.storage.delete, f_name)
         mtime = self.storage.modified_time(f_name)
 
-        self.assertEqual(mtime, datetime.fromtimestamp(
+        self.assertEqual(mtime, datetime.fromtimestamp(os.path.getmtime(self.storage.path(f_name))))
-            os.path.getmtime(self.storage.path(f_name))))
         self.assertLess(datetime.now() - self.storage.modified_time(f_name), timedelta(seconds=2))
 
-        self.storage.delete(f_name)
-
     def test_file_save_without_name(self):
         """
         File storage extracts the filename from the content object if no
@@ -473,6 +622,26 @@ class CustomStorageTests(FileStorageTests):
         self.storage.delete(second)
 
 
+class CustomStorageLegacyDatetimeHandling(FileSystemStorage):
+    # Use the legacy accessed_time() et al from FileSystemStorage and the
+    # shim get_accessed_time() et al from the Storage baseclass. Both of those
+    # raise warnings, so the testcase class ignores them all.
+
+    def get_accessed_time(self, name):
+        return super(FileSystemStorage, self).get_accessed_time(name)
+
+    def get_created_time(self, name):
+        return super(FileSystemStorage, self).get_created_time(name)
+
+    def get_modified_time(self, name):
+        return super(FileSystemStorage, self).get_modified_time(name)
+
+
+@ignore_warnings(category=RemovedInDjango20Warning)
+class CustomStorageLegacyDatetimeHandlingTests(FileStorageTests):
+    storage_class = CustomStorageLegacyDatetimeHandling
+
+
 class FileFieldStorageTests(TestCase):
     def tearDown(self):
         shutil.rmtree(temp_storage_location)

tests/staticfiles_tests/storage.py

@@ -2,12 +2,12 @@ from datetime import datetime
 
 from django.contrib.staticfiles.storage import CachedStaticFilesStorage
 from django.core.files import storage
+from django.utils import timezone
 
 
 class DummyStorage(storage.Storage):
     """
-    A storage class that does implement modified_time() but raises
+    A storage class that implements get_modified_time().
-    NotImplementedError when calling
     """
     def _save(self, name, content):
         return 'dummy'
@@ -18,8 +18,8 @@ class DummyStorage(storage.Storage):
     def exists(self, name):
         pass
 
-    def modified_time(self, name):
+    def get_modified_time(self, name):
-        return datetime.date(1970, 1, 1)
+        return datetime.datetime(1970, 1, 1, tzinfo=timezone.utc)
 
 
 class SimpleCachedStaticFilesStorage(CachedStaticFilesStorage):