cached_property works wrong with inheritance

[ystakhovsky]

class Parent(object):
  @cached_property
  def test(self):
    return 1


class Child(Parent):
  @cached_property
  def test(self):
    result = super(Child, self).test
    result = result / 0
    return result


child_instance = Child()
print(child_instance.test)
# gives a traceback

print(child_instance.test)
# prints "1"

Here is a quick-fix solution:

diff --git a/cached_property.py b/cached_property.py
index 67fa01a..6122eab 100644
--- a/cached_property.py
+++ b/cached_property.py
@@ -32,7 +32,13 @@ class cached_property(object):
         if asyncio and asyncio.iscoroutinefunction(self.func):
             return self._wrap_in_coroutine(obj)
 
-        value = obj.__dict__[self.func.__name__] = self.func(obj)
+        try:
+            value = self.func(obj)
+        except Exception:
+            obj.__dict__.pop(self.func.__name__, None)
+            raise
+
+        obj.__dict__[self.func.__name__] = value
         return value
 
     def _wrap_in_coroutine(self, obj):
@@ -69,7 +75,12 @@ class threaded_cached_property(object):
 
             except KeyError:
                 # if not, do the calculation and release the lock
-                return obj_dict.setdefault(name, self.func(obj))
+                try:
+                    value = self.func(obj)
+                except Exception:
+                    obj_dict.pop(name, None)
+                    raise
+                return obj_dict.setdefault(name, value)
 
 
 class cached_property_with_ttl(object):
@@ -108,7 +119,11 @@ class cached_property_with_ttl(object):
             if not ttl_expired:
                 return value
 
-        value = self.func(obj)
+        try:
+            value = self.func(obj)
+        except Exception:
+            obj_dict.pop(name, None)
+            raise
         obj_dict[name] = (value, now)
         return value
 
diff --git a/tests/test_cached_property.py b/tests/test_cached_property.py
index 5082416..e3499b2 100644
--- a/tests/test_cached_property.py
+++ b/tests/test_cached_property.py
@@ -88,6 +88,23 @@ class TestCachedProperty(unittest.TestCase):
         # rather than through an instance.
         self.assertTrue(isinstance(Check.add_cached, self.cached_property_factory))
 
+    def test_error_on_inheritance(self):
+        class CheckWithInheritance(CheckFactory(self.cached_property_factory)):
+            @self.cached_property_factory
+            def add_cached(inst):
+                return super(CheckWithInheritance, inst).add_cached / 0
+
+        check = CheckWithInheritance()
+        stub_to_check = object()
+
+        result = stub_to_check
+        with self.assertRaises(ZeroDivisionError):
+            result = check.add_cached
+        with self.assertRaises(ZeroDivisionError):
+            result = check.add_cached
+
+        self.assertEqual(result, stub_to_check)
+
     def test_reset_cached_property(self):
         Check = CheckFactory(self.cached_property_factory)
         check = Check()