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)

django/core/management/commands/loaddata.py

@@ -14,8 +14,9 @@ from django.core.management.color import no_style
 from django.db import (connections, router, transaction, DEFAULT_DB_ALIAS,
       IntegrityError, DatabaseError)
 from django.db.models import get_app_paths
+from django.utils import lru_cache
 from django.utils.encoding import force_text
-from django.utils.functional import cached_property, memoize
+from django.utils.functional import cached_property
 from django.utils._os import upath
 from itertools import product
 
@@ -164,7 +165,8 @@ class Command(BaseCommand):
                     RuntimeWarning
                 )
 
-    def _find_fixtures(self, fixture_label):
+    @lru_cache.lru_cache(maxsize=None)
+    def find_fixtures(self, fixture_label):
         """
         Finds fixture files for a given label.
         """
@@ -220,9 +222,6 @@ class Command(BaseCommand):
 
         return fixture_files
 
-    _label_to_fixtures_cache = {}
-    find_fixtures = memoize(_find_fixtures, _label_to_fixtures_cache, 2)
-
     @cached_property
     def fixture_dirs(self):
         """

django/core/urlresolvers.py

@@ -16,18 +16,14 @@ from django.http import Http404
 from django.core.exceptions import ImproperlyConfigured, ViewDoesNotExist
 from django.utils.datastructures import MultiValueDict
 from django.utils.encoding import force_str, force_text, iri_to_uri
-from django.utils.functional import memoize, lazy
+from django.utils.functional import lazy
 from django.utils.http import urlquote
 from django.utils.module_loading import module_has_submodule
 from django.utils.regex_helper import normalize
-from django.utils import six
+from django.utils import six, lru_cache
 from django.utils.translation import get_language
 
 
-_resolver_cache = {}  # Maps URLconf modules to RegexURLResolver instances.
-_ns_resolver_cache = {}  # Maps namespaces to RegexURLResolver instances.
-_callable_cache = {}  # Maps view and url pattern names to their view functions.
-
 # SCRIPT_NAME prefixes for each thread are stored here. If there's no entry for
 # the current thread (which is the only one we ever access), it is assumed to
 # be empty.
@@ -80,6 +76,7 @@ class NoReverseMatch(Exception):
     pass
 
 
+@lru_cache.lru_cache(maxsize=None)
 def get_callable(lookup_view, can_fail=False):
     """
     Convert a string version of a function name to the callable object.
@@ -119,17 +116,17 @@ def get_callable(lookup_view, can_fail=False):
                         "Could not import %s. View does not exist in module %s." %
                         (lookup_view, mod_name))
     return lookup_view
-get_callable = memoize(get_callable, _callable_cache, 1)
 
 
+@lru_cache.lru_cache(maxsize=None)
 def get_resolver(urlconf):
     if urlconf is None:
         from django.conf import settings
         urlconf = settings.ROOT_URLCONF
     return RegexURLResolver(r'^/', urlconf)
-get_resolver = memoize(get_resolver, _resolver_cache, 1)
 
 
+@lru_cache.lru_cache(maxsize=None)
 def get_ns_resolver(ns_pattern, resolver):
     # Build a namespaced resolver for the given parent urlconf pattern.
     # This makes it possible to have captured parameters in the parent
@@ -137,7 +134,6 @@ def get_ns_resolver(ns_pattern, resolver):
     ns_resolver = RegexURLResolver(ns_pattern,
                                           resolver.url_patterns)
     return RegexURLResolver(r'^/', [ns_resolver])
-get_ns_resolver = memoize(get_ns_resolver, _ns_resolver_cache, 2)
 
 
 def get_mod_func(callback):
@@ -523,12 +519,9 @@ reverse_lazy = lazy(reverse, str)
 
 
 def clear_url_caches():
-    global _resolver_cache
+    get_callable.cache_clear()
-    global _ns_resolver_cache
+    get_resolver.cache_clear()
-    global _callable_cache
+    get_ns_resolver.cache_clear()
-    _resolver_cache.clear()
-    _ns_resolver_cache.clear()
-    _callable_cache.clear()
 
 
 def set_script_prefix(prefix):

django/test/utils.py

@@ -427,7 +427,7 @@ class TransRealMixin(object):
         trans_real._translations = {}
         trans_real._active = local()
         trans_real._default = None
-        trans_real._checked_languages = {}
+        trans_real.check_for_language.cache_clear()
 
     def tearDown(self):
         self.flush_caches()

django/utils/functional.py

@@ -2,6 +2,7 @@ import copy
 import operator
 from functools import wraps
 import sys
+import warnings
 
 from django.utils import six
 from django.utils.six.moves import copyreg
@@ -24,6 +25,10 @@ def memoize(func, cache, num_args):
 
     Only the first num_args are considered when creating the key.
     """
+    warnings.warn(u"memoize wrapper is deprecated and will be removed in "
+                  u"Django 1.9. Use django.utils.lru_cache instead.",
+                  PendingDeprecationWarning, 2)
+
     @wraps(func)
     def wrapper(*args):
         mem_args = args[:num_args]

django/utils/lru_cache.py

@@ -0,0 +1,173 @@
+try:
+    from functools import lru_cache
+
+except ImportError:
+    # backport of Python's 3.2 lru_cache, written by Raymond Hettinger and
+    # licensed under MIT license, from:
+    # <http://code.activestate.com/recipes/578078-py26-and-py30-backport-of-python-33s-lru-cache/>
+    # Should be removed when Django only supports Python 3.2 and above.
+
+    from collections import namedtuple
+    from functools import update_wrapper
+    from threading import RLock
+
+    _CacheInfo = namedtuple("CacheInfo", ["hits", "misses", "maxsize", "currsize"])
+
+    class _HashedSeq(list):
+        __slots__ = 'hashvalue'
+
+        def __init__(self, tup, hash=hash):
+            self[:] = tup
+            self.hashvalue = hash(tup)
+
+        def __hash__(self):
+            return self.hashvalue
+
+    def _make_key(args, kwds, typed,
+                 kwd_mark = (object(),),
+                 fasttypes = {int, str, frozenset, type(None)},
+                 sorted=sorted, tuple=tuple, type=type, len=len):
+        'Make a cache key from optionally typed positional and keyword arguments'
+        key = args
+        if kwds:
+            sorted_items = sorted(kwds.items())
+            key += kwd_mark
+            for item in sorted_items:
+                key += item
+        if typed:
+            key += tuple(type(v) for v in args)
+            if kwds:
+                key += tuple(type(v) for k, v in sorted_items)
+        elif len(key) == 1 and type(key[0]) in fasttypes:
+            return key[0]
+        return _HashedSeq(key)
+
+    def lru_cache(maxsize=100, typed=False):
+        """Least-recently-used cache decorator.
+
+        If *maxsize* is set to None, the LRU features are disabled and the cache
+        can grow without bound.
+
+        If *typed* is True, arguments of different types will be cached separately.
+        For example, f(3.0) and f(3) will be treated as distinct calls with
+        distinct results.
+
+        Arguments to the cached function must be hashable.
+
+        View the cache statistics named tuple (hits, misses, maxsize, currsize) with
+        f.cache_info().  Clear the cache and statistics with f.cache_clear().
+        Access the underlying function with f.__wrapped__.
+
+        See:  http://en.wikipedia.org/wiki/Cache_algorithms#Least_Recently_Used
+
+        """
+
+        # Users should only access the lru_cache through its public API:
+        #       cache_info, cache_clear, and f.__wrapped__
+        # The internals of the lru_cache are encapsulated for thread safety and
+        # to allow the implementation to change (including a possible C version).
+
+        def decorating_function(user_function):
+
+            cache = dict()
+            stats = [0, 0]                  # make statistics updateable non-locally
+            HITS, MISSES = 0, 1             # names for the stats fields
+            make_key = _make_key
+            cache_get = cache.get           # bound method to lookup key or return None
+            _len = len                      # localize the global len() function
+            lock = RLock()                  # because linkedlist updates aren't threadsafe
+            root = []                       # root of the circular doubly linked list
+            root[:] = [root, root, None, None]      # initialize by pointing to self
+            nonlocal_root = [root]                  # make updateable non-locally
+            PREV, NEXT, KEY, RESULT = 0, 1, 2, 3    # names for the link fields
+
+            if maxsize == 0:
+
+                def wrapper(*args, **kwds):
+                    # no caching, just do a statistics update after a successful call
+                    result = user_function(*args, **kwds)
+                    stats[MISSES] += 1
+                    return result
+
+            elif maxsize is None:
+
+                def wrapper(*args, **kwds):
+                    # simple caching without ordering or size limit
+                    key = make_key(args, kwds, typed)
+                    result = cache_get(key, root)   # root used here as a unique not-found sentinel
+                    if result is not root:
+                        stats[HITS] += 1
+                        return result
+                    result = user_function(*args, **kwds)
+                    cache[key] = result
+                    stats[MISSES] += 1
+                    return result
+
+            else:
+
+                def wrapper(*args, **kwds):
+                    # size limited caching that tracks accesses by recency
+                    key = make_key(args, kwds, typed) if kwds or typed else args
+                    with lock:
+                        link = cache_get(key)
+                        if link is not None:
+                            # record recent use of the key by moving it to the front of the list
+                            root, = nonlocal_root
+                            link_prev, link_next, key, result = link
+                            link_prev[NEXT] = link_next
+                            link_next[PREV] = link_prev
+                            last = root[PREV]
+                            last[NEXT] = root[PREV] = link
+                            link[PREV] = last
+                            link[NEXT] = root
+                            stats[HITS] += 1
+                            return result
+                    result = user_function(*args, **kwds)
+                    with lock:
+                        root, = nonlocal_root
+                        if key in cache:
+                            # getting here means that this same key was added to the
+                            # cache while the lock was released.  since the link
+                            # update is already done, we need only return the
+                            # computed result and update the count of misses.
+                            pass
+                        elif _len(cache) >= maxsize:
+                            # use the old root to store the new key and result
+                            oldroot = root
+                            oldroot[KEY] = key
+                            oldroot[RESULT] = result
+                            # empty the oldest link and make it the new root
+                            root = nonlocal_root[0] = oldroot[NEXT]
+                            oldkey = root[KEY]
+                            oldvalue = root[RESULT]
+                            root[KEY] = root[RESULT] = None
+                            # now update the cache dictionary for the new links
+                            del cache[oldkey]
+                            cache[key] = oldroot
+                        else:
+                            # put result in a new link at the front of the list
+                            last = root[PREV]
+                            link = [last, root, key, result]
+                            last[NEXT] = root[PREV] = cache[key] = link
+                        stats[MISSES] += 1
+                    return result
+
+            def cache_info():
+                """Report cache statistics"""
+                with lock:
+                    return _CacheInfo(stats[HITS], stats[MISSES], maxsize, len(cache))
+
+            def cache_clear():
+                """Clear the cache and cache statistics"""
+                with lock:
+                    cache.clear()
+                    root = nonlocal_root[0]
+                    root[:] = [root, root, None, None]
+                    stats[:] = [0, 0]
+
+            wrapper.__wrapped__ = user_function
+            wrapper.cache_info = cache_info
+            wrapper.cache_clear = cache_clear
+            return update_wrapper(wrapper, user_function)
+
+        return decorating_function

django/utils/translation/trans_real.py

@@ -14,10 +14,9 @@ import warnings
 from django.dispatch import receiver
 from django.test.signals import setting_changed
 from django.utils.encoding import force_str, force_text
-from django.utils.functional import memoize
 from django.utils._os import upath
 from django.utils.safestring import mark_safe, SafeData
-from django.utils import six
+from django.utils import six, lru_cache
 from django.utils.six import StringIO
 from django.utils.translation import TranslatorCommentWarning, trim_whitespace
 
@@ -33,7 +32,6 @@ _default = None
 # This is a cache for normalized accept-header languages to prevent multiple
 # file lookups when checking the same locale on repeated requests.
 _accepted = {}
-_checked_languages = {}
 
 # magic gettext number to separate context from message
 CONTEXT_SEPARATOR = "\x04"
@@ -390,6 +388,7 @@ def all_locale_paths():
     return [globalpath] + list(settings.LOCALE_PATHS)
 
 
+@lru_cache.lru_cache(maxsize=None)
 def check_for_language(lang_code):
     """
     Checks whether there is a global language file for the given language
@@ -401,7 +400,6 @@ def check_for_language(lang_code):
         if gettext_module.find('django', path, [to_locale(lang_code)]) is not None:
             return True
     return False
-check_for_language = memoize(check_for_language, _checked_languages, 1)
 
 
 def get_supported_language_variant(lang_code, supported=None, strict=False):

docs/internals/deprecation.txt

@@ -479,6 +479,8 @@ these changes.
 * The ``zh-cn`` and ``zh-tw`` language codes will be removed and have been
   replaced by the ``zh-hans`` and ``zh-hant`` language code respectively.
 
+* The internal ``django.utils.functional.memoize`` will be removed.
+
 2.0
 ---
 

docs/releases/1.7.txt

@@ -752,3 +752,13 @@ recently introduced language codes ``zh-hans`` and ``zh-hant`` respectively.
 If you use these language codes, you should rename the locale directories
 and update your settings to reflect these changes. The deprecated language
 codes will be removed in Django 1.9.
+
+``django.utils.functional.memoize`` function
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The function ``memoize`` is deprecated and should be replaced by the
+``functools.lru_cache`` decorator (available from Python 3.2 onwards).
+
+Django ships a backport of this decorator for older Python versions and it's
+available at ``django.utils.lru_cache.lru_cache``. The deprecated function will
+be removed in Django 1.9.

tests/decorators/tests.py

@@ -1,5 +1,6 @@
 from functools import wraps
 from unittest import TestCase
+import warnings
 
 from django.contrib.admin.views.decorators import staff_member_required
 from django.contrib.auth.decorators import login_required, permission_required, user_passes_test
@@ -58,11 +59,14 @@ full_decorator = compose(
     staff_member_required,
 
     # django.utils.functional
-    lambda f: memoize(f, {}, 1),
     allow_lazy,
     lazy,
 )
 
+# suppress the deprecation warning of memoize
+with warnings.catch_warnings(record=True):
+    fully_decorated = memoize(fully_decorated, {}, 1)
+
 fully_decorated = full_decorator(fully_decorated)
 
 

tests/deprecation/tests.py

@@ -4,6 +4,7 @@ import warnings
 from django.test import SimpleTestCase, RequestFactory, override_settings
 from django.utils import six, translation
 from django.utils.deprecation import RenameMethodsBase
+from django.utils.functional import memoize
 
 
 class RenameManagerMethods(RenameMethodsBase):
@@ -205,3 +206,18 @@ class DeprecatedChineseLanguageCodes(SimpleTestCase):
                 "The use of the language code 'zh-tw' is deprecated. "
                 "Please use the 'zh-hant' translation instead.",
             ])
+
+
+class DeprecatingMemoizeTest(SimpleTestCase):
+    def test_deprecated_memoize(self):
+        """
+        Ensure the correct warning is raised when memoize is used.
+        """
+        warnings.simplefilter('always')
+
+        with warnings.catch_warnings(record=True) as recorded:
+            memoize(lambda x: x, {}, 1)
+            msg = str(recorded.pop().message)
+            self.assertEqual(msg,
+                'memoize wrapper is deprecated and will be removed in Django '
+                '1.9. Use django.utils.lru_cache instead.')

tests/staticfiles_tests/tests.py

@@ -55,7 +55,7 @@ class BaseStaticFilesTestCase(object):
         storage.staticfiles_storage._wrapped = empty
         # Clear the cached staticfile finders, so they are reinitialized every
         # run and pick up changes in settings.STATICFILES_DIRS.
-        finders._finders.clear()
+        finders.get_finder.cache_clear()
 
         testfiles_path = os.path.join(TEST_ROOT, 'apps', 'test', 'static', 'test')
         # To make sure SVN doesn't hangs itself with the non-ASCII characters
@@ -561,7 +561,7 @@ class TestCollectionCachedStorage(BaseCollectionTestCase,
         Test that post_processing indicates the origin of the error when it
         fails. Regression test for #18986.
         """
-        finders._finders.clear()
+        finders.get_finder.cache_clear()
         err = six.StringIO()
         with self.assertRaises(Exception):
             call_command('collectstatic', interactive=False, verbosity=0, stderr=err)
@@ -756,6 +756,15 @@ class TestMiscFinder(TestCase):
         self.assertRaises(ImproperlyConfigured,
             finders.get_finder, 'foo.bar.FooBarFinder')
 
+    def test_cache(self):
+        finders.get_finder.cache_clear()
+        for n in range(10):
+            finders.get_finder(
+                'django.contrib.staticfiles.finders.FileSystemFinder')
+        cache_info = finders.get_finder.cache_info()
+        self.assertEqual(cache_info.hits, 9)
+        self.assertEqual(cache_info.currsize, 1)
+
     @override_settings(STATICFILES_DIRS='a string')
     def test_non_tuple_raises_exception(self):
         """

tests/urlpatterns_reverse/tests.py

@@ -17,6 +17,7 @@ from django.test.utils import override_settings
 from django.utils import six
 
 from . import urlconf_outer, middleware, views
+from .views import empty_view
 
 
 resolve_test_data = (
@@ -662,9 +663,17 @@ class ErroneousViewTests(TestCase):
 
 class ViewLoadingTests(TestCase):
     def test_view_loading(self):
+        self.assertEqual(get_callable('urlpatterns_reverse.views.empty_view'),
+                         empty_view)
+
+        # passing a callable should return the callable
+        self.assertEqual(get_callable(empty_view), empty_view)
+
+    def test_exceptions(self):
         # A missing view (identified by an AttributeError) should raise
         # ViewDoesNotExist, ...
-        six.assertRaisesRegex(self, ViewDoesNotExist, ".*View does not exist in.*",
+        six.assertRaisesRegex(self, ViewDoesNotExist,
+                              ".*View does not exist in.*",
                               get_callable,
                               'urlpatterns_reverse.views.i_should_not_exist')
         # ... but if the AttributeError is caused by something else don't