def test_cached_property_slot_wrong_type_set(self):
"""apply a cached property from one type to another"""
class C:
__slots__ = ("abc", )
class D:
pass
D.abc = cached_property(lambda self: 42, C.abc)
a = D()
with self.assertRaises(TypeError):
print(a.abc)
def test_cached_property_slot(self):
class C:
__slots__ = ("f", "calls")
def __init__(self):
self.calls = 0
def f(self):
self.calls += 1
return 42
C.f = cached_property(f, C.f)
a = C()
self.assertEqual(a.f, 42)
self.assertEqual(a.calls, 1)
self.assertEqual(a.f, 42)
self.assertEqual(a.calls, 1)
def test_cached_property_slot_set_del(self):
class C:
__slots__ = ("f", "calls")
def __init__(self):
self.calls = 0
def f(self):
self.calls += 1
return 42
C.f = cached_property(f, C.f)
a = C()
a.f = 100
self.assertEqual(a.f, 100)
self.assertEqual(a.calls, 0)
del a.f
with self.assertRaises(AttributeError):
del a.f
self.assertEqual(a.f, 42)
self.assertEqual(a.calls, 1)
def test_cached_property_readonly_descriptor(self):
with self.assertRaises(TypeError):
cached_property(lambda self: 42, range.start)
def test_cached_property_incompatible_descriptor(self):
with self.assertRaises(TypeError):
cached_property(lambda self: 42, GeneratorType.gi_frame)
def test_cached_property_non_descriptor(self):
with self.assertRaises(TypeError):
cached_property(lambda self: 42, 42)