From f1bb3ee001077db3905a2efe67e397be55818168 Mon Sep 17 00:00:00 2001
From: Bertrand Bordage <bordage.bertrand@gmail.com>
Date: Sun, 5 Oct 2014 03:11:26 +0200
Subject: [PATCH] Adds a context manager & decorator to dynamically override
 settings.

---
 README.rst           | 23 +++++++++++++++++++----
 cachalot/settings.py | 24 ++++++++++++++++++++++++
 cachalot/tests.py    | 20 +++++++++++++++-----
 3 files changed, 58 insertions(+), 9 deletions(-)

diff --git a/README.rst b/README.rst
index 3074fa4..edd56d0 100644
--- a/README.rst
+++ b/README.rst
@@ -53,12 +53,27 @@ Setting              Default value Description
 .. |CACHES| replace:: ``CACHES``
 .. _CACHES: https://docs.djangoproject.com/en/1.7/ref/settings/#std:setting-CACHES
 
-.. note:: Settings can be changed at any moment during runtime like this:
+These settings can be changed whenever you want.
+You have to use ``cachalot_settings`` as a context manager, a decorator,
+or simply by changing its attributes:
 
-   .. code:: python
+.. code:: python
 
-       from cachalot.settings import cachalot_settings
-       cachalot_settings.CACHALOT_CACHE = 'another_cache'
+    from cachalot.settings import cachalot_settings
+
+    with cachalot_settings(CACHALOT_ENABLED=False):
+        # SQL queries are not cached in this block
+
+    @cachalot_settings(CACHALOT_CACHE='another_cache')
+    def your_function():
+        # What’s in this function uses another cache
+
+    # Globally disables SQL caching until you set it back to True
+    cachalot_settings.CACHALOT_ENABLED = False
+
+In tests, you can use
+`Django’s testing tools <https://docs.djangoproject.com/en/1.7/topics/testing/tools/#overriding-settings>`_
+as well as ``cachalot_settings``.  They will both work the same.
 
 
 Limits
diff --git a/cachalot/settings.py b/cachalot/settings.py
index 9c79eaf..e383508 100644
--- a/cachalot/settings.py
+++ b/cachalot/settings.py
@@ -1,6 +1,27 @@
 from django.conf import settings
 
 
+class SettingsOverrider(object):
+    def __init__(self, settings, overrides):
+        self.settings = settings
+        self.overrides = overrides
+        self.originals = {k: getattr(self.settings, k) for k in self.overrides}
+
+    def __enter__(self):
+        for k, v in self.overrides.items():
+            setattr(self.settings, k, v)
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        for k, v in self.originals.items():
+            setattr(self.settings, k, v)
+
+    def __call__(self, func):
+        def inner(*args, **kwargs):
+            with self:
+                return func(*args, **kwargs)
+        return inner
+
+
 class Settings(object):
     CACHALOT_ENABLED = True
     CACHALOT_CACHE = 'default'
@@ -10,5 +31,8 @@ class Settings(object):
             return getattr(settings, item)
         return super(Settings, self).__getattribute__(item)
 
+    def __call__(self, **kwargs):
+        return SettingsOverrider(self, kwargs)
+
 
 cachalot_settings = Settings()
diff --git a/cachalot/tests.py b/cachalot/tests.py
index 574544f..d6a2cd0 100644
--- a/cachalot/tests.py
+++ b/cachalot/tests.py
@@ -1,6 +1,9 @@
 # coding: utf-8
 
 from __future__ import unicode_literals
+from cachalot.settings import cachalot_settings
+
+
 try:
     from unittest import skip, skipIf
 except ImportError:  # For Python 2.6
@@ -1178,14 +1181,21 @@ class AtomicTestCase(TestCase):
 
 
 class SettingsTestCase(TestCase):
+    @cachalot_settings(CACHALOT_ENABLED=False)
+    def test_decorator(self):
+        with self.assertNumQueries(1):
+            list(Test.objects.all())
+        with self.assertNumQueries(1):
+            list(Test.objects.all())
+
     def test_enabled(self):
-        with self.settings(CACHALOT_ENABLED=True):
+        with cachalot_settings(CACHALOT_ENABLED=True):
             with self.assertNumQueries(1):
                 list(Test.objects.all())
             with self.assertNumQueries(0):
                 list(Test.objects.all())
 
-        with self.settings(CACHALOT_ENABLED=False):
+        with cachalot_settings(CACHALOT_ENABLED=False):
             with self.assertNumQueries(1):
                 list(Test.objects.all())
             with self.assertNumQueries(1):
@@ -1194,7 +1204,7 @@ class SettingsTestCase(TestCase):
         with self.assertNumQueries(0):
             list(Test.objects.all())
 
-        with self.settings(CACHALOT_ENABLED=False):
+        with cachalot_settings(CACHALOT_ENABLED=False):
             with self.assertNumQueries(1):
                 t = Test.objects.create(name='test')
         with self.assertNumQueries(1):
@@ -1204,7 +1214,7 @@ class SettingsTestCase(TestCase):
     @skipIf(len(settings.CACHES) == 1,
             'We can’t change the cache used since there’s only one configured')
     def test_cache(self):
-        with self.settings(CACHALOT_CACHE='default'):
+        with cachalot_settings(CACHALOT_CACHE='default'):
             with self.assertNumQueries(1):
                 list(Test.objects.all())
             with self.assertNumQueries(0):
@@ -1212,7 +1222,7 @@ class SettingsTestCase(TestCase):
 
         other_cache = [k for k in settings.CACHES if k != 'default'][0]
 
-        with self.settings(CACHALOT_CACHE=other_cache):
+        with cachalot_settings(CACHALOT_CACHE=other_cache):
             with self.assertNumQueries(1):
                 list(Test.objects.all())
             with self.assertNumQueries(0):