Fixed #21351 -- Replaced memoize with Python's lru_cache.

Replaced the custom, untested memoize with a similar decorator from Python's
3.2 stdlib. Although some minor performance degradation (see ticket), it is
expected that in the long run lru_cache will outperform memoize once it is
implemented in C.

Thanks to EvilDMP for the report and Baptiste Mispelon for the idea of
replacing memoize with lru_cache.

django/contrib/staticfiles/finders.py

@@ -4,16 +4,14 @@ import os
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.core.files.storage import default_storage, Storage, FileSystemStorage
-from django.utils.functional import empty, memoize, LazyObject
+from django.utils.functional import empty, LazyObject
 from django.utils.module_loading import import_by_path
 from django.utils._os import safe_join
-from django.utils import six
+from django.utils import six, lru_cache
 
 from django.contrib.staticfiles import utils
 from django.contrib.staticfiles.storage import AppStaticStorage
 
-_finders = OrderedDict()
-
 
 class BaseFinder(object):
     """
@@ -254,7 +252,8 @@ def get_finders():
         yield get_finder(finder_path)
 
 
-def _get_finder(import_path):
+@lru_cache.lru_cache(maxsize=None)
+def get_finder(import_path):
     """
     Imports the staticfiles finder class described by import_path, where
     import_path is the full Python path to the class.
@@ -264,4 +263,3 @@ def _get_finder(import_path):
         raise ImproperlyConfigured('Finder "%s" is not a subclass of "%s"' %
                                    (Finder, BaseFinder))
     return Finder()
-get_finder = memoize(_get_finder, _finders, 1)