Fixed django#19872

Made cached_property to behave as property when accessed via class.

Author: oinopion

django/utils/functional.py

@@ -39,7 +39,9 @@ class cached_property(object):
  def __init__(self, func):
  self.func = func
 
- def __get__(self, instance, type):
+ def __get__(self, instance, type=None):
+ if instance is None:
+ return self
  res = instance.__dict__[self.func.__name__] = self.func(instance)
  return res
 

tests/regressiontests/utils/functional.py

@@ -1,5 +1,5 @@
 from django.utils import unittest
-from django.utils.functional import lazy, lazy_property
+from django.utils.functional import lazy, lazy_property, cached_property
 
 
 class FunctionalTestCase(unittest.TestCase):
@@ -37,3 +37,30 @@ def _get_do(self):
 
  self.assertRaises(NotImplementedError, lambda: A().do)
  self.assertEqual(B().do, 'DO IT')
+
+ def test_cached_property(self):
+ """
+ Test that cached_property caches its value,
+ and that it behaves like a property
+ """
+
+ class A(object):
+
+ @cached_property
+ def value(self):
+ return 1, object()
+
+ a = A()
+
+ # check that it is cached
+ self.assertEqual(a.value, a.value)
+
+ # check that it returns the right thing
+ self.assertEqual(a.value[0], 1)
+
+ # check that state isn't shared between instances
+ a2 = A()
+ self.assertNotEqual(a.value, a2.value)
+
+ # check that it behaves like a property when there's no instance
+ self.assertIsInstance(A.value, cached_property)