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authorCarl Meyer <carl@oddbird.net>2018-08-28 07:11:56 (GMT)
committerNick Coghlan <ncoghlan@gmail.com>2018-08-28 07:11:56 (GMT)
commitd658deac6060ee92b449a3bf424b460eafd99f3e (patch)
treeb20a3a288b17dd17fbd5e555f139b2c1df80bcb7 /Lib/test
parent216b745eafa7cd4a683a8405dcfbd7f5567f504c (diff)
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bpo-21145: Add cached_property decorator in functools (#6982)
Robust caching of calculated properties is harder than it looks at first glance, so add a solid, well-tested implementation to the standard library.
Diffstat (limited to 'Lib/test')
-rw-r--r--Lib/test/test_functools.py166
1 files changed, 166 insertions, 0 deletions
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index 10bf0a2..200a5eb 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -2313,5 +2313,171 @@ class TestSingleDispatch(unittest.TestCase):
with self.assertRaisesRegex(TypeError, msg):
f()
+
+class CachedCostItem:
+ _cost = 1
+
+ def __init__(self):
+ self.lock = py_functools.RLock()
+
+ @py_functools.cached_property
+ def cost(self):
+ """The cost of the item."""
+ with self.lock:
+ self._cost += 1
+ return self._cost
+
+
+class OptionallyCachedCostItem:
+ _cost = 1
+
+ def get_cost(self):
+ """The cost of the item."""
+ self._cost += 1
+ return self._cost
+
+ cached_cost = py_functools.cached_property(get_cost)
+
+
+class CachedCostItemWait:
+
+ def __init__(self, event):
+ self._cost = 1
+ self.lock = py_functools.RLock()
+ self.event = event
+
+ @py_functools.cached_property
+ def cost(self):
+ self.event.wait(1)
+ with self.lock:
+ self._cost += 1
+ return self._cost
+
+
+class CachedCostItemWithSlots:
+ __slots__ = ('_cost')
+
+ def __init__(self):
+ self._cost = 1
+
+ @py_functools.cached_property
+ def cost(self):
+ raise RuntimeError('never called, slots not supported')
+
+
+class TestCachedProperty(unittest.TestCase):
+ def test_cached(self):
+ item = CachedCostItem()
+ self.assertEqual(item.cost, 2)
+ self.assertEqual(item.cost, 2) # not 3
+
+ def test_cached_attribute_name_differs_from_func_name(self):
+ item = OptionallyCachedCostItem()
+ self.assertEqual(item.get_cost(), 2)
+ self.assertEqual(item.cached_cost, 3)
+ self.assertEqual(item.get_cost(), 4)
+ self.assertEqual(item.cached_cost, 3)
+
+ def test_threaded(self):
+ go = threading.Event()
+ item = CachedCostItemWait(go)
+
+ num_threads = 3
+
+ orig_si = sys.getswitchinterval()
+ sys.setswitchinterval(1e-6)
+ try:
+ threads = [
+ threading.Thread(target=lambda: item.cost)
+ for k in range(num_threads)
+ ]
+ with support.start_threads(threads):
+ go.set()
+ finally:
+ sys.setswitchinterval(orig_si)
+
+ self.assertEqual(item.cost, 2)
+
+ def test_object_with_slots(self):
+ item = CachedCostItemWithSlots()
+ with self.assertRaisesRegex(
+ TypeError,
+ "No '__dict__' attribute on 'CachedCostItemWithSlots' instance to cache 'cost' property.",
+ ):
+ item.cost
+
+ def test_immutable_dict(self):
+ class MyMeta(type):
+ @py_functools.cached_property
+ def prop(self):
+ return True
+
+ class MyClass(metaclass=MyMeta):
+ pass
+
+ with self.assertRaisesRegex(
+ TypeError,
+ "The '__dict__' attribute on 'MyMeta' instance does not support item assignment for caching 'prop' property.",
+ ):
+ MyClass.prop
+
+ def test_reuse_different_names(self):
+ """Disallow this case because decorated function a would not be cached."""
+ with self.assertRaises(RuntimeError) as ctx:
+ class ReusedCachedProperty:
+ @py_functools.cached_property
+ def a(self):
+ pass
+
+ b = a
+
+ self.assertEqual(
+ str(ctx.exception.__context__),
+ str(TypeError("Cannot assign the same cached_property to two different names ('a' and 'b')."))
+ )
+
+ def test_reuse_same_name(self):
+ """Reusing a cached_property on different classes under the same name is OK."""
+ counter = 0
+
+ @py_functools.cached_property
+ def _cp(_self):
+ nonlocal counter
+ counter += 1
+ return counter
+
+ class A:
+ cp = _cp
+
+ class B:
+ cp = _cp
+
+ a = A()
+ b = B()
+
+ self.assertEqual(a.cp, 1)
+ self.assertEqual(b.cp, 2)
+ self.assertEqual(a.cp, 1)
+
+ def test_set_name_not_called(self):
+ cp = py_functools.cached_property(lambda s: None)
+ class Foo:
+ pass
+
+ Foo.cp = cp
+
+ with self.assertRaisesRegex(
+ TypeError,
+ "Cannot use cached_property instance without calling __set_name__ on it.",
+ ):
+ Foo().cp
+
+ def test_access_from_class(self):
+ self.assertIsInstance(CachedCostItem.cost, py_functools.cached_property)
+
+ def test_doc(self):
+ self.assertEqual(CachedCostItem.cost.__doc__, "The cost of the item.")
+
+
if __name__ == '__main__':
unittest.main()