bpo-33175: dataclasses should look up __set_name__ on class, not instance (GH-6305)
diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 8c197fe..bd7252c 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -248,11 +248,11 @@
# the default value, so the end result is a descriptor that had
# __set_name__ called on it at the right time.
def __set_name__(self, owner, name):
- func = getattr(self.default, '__set_name__', None)
+ func = getattr(type(self.default), '__set_name__', None)
if func:
# There is a __set_name__ method on the descriptor,
# call it.
- func(owner, name)
+ func(self.default, owner, name)
class _DataclassParams:
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 2745eaf..5cd424c 100755
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -2705,7 +2705,7 @@
# Create a descriptor.
class D:
def __set_name__(self, owner, name):
- self.name = name
+ self.name = name + 'x'
def __get__(self, instance, owner):
if instance is not None:
return 1
@@ -2716,7 +2716,7 @@
@dataclass
class C:
c: int=D()
- self.assertEqual(C.c.name, 'c')
+ self.assertEqual(C.c.name, 'cx')
# Now test with a default value and init=False, which is the
# only time this is really meaningful. If not using
@@ -2724,7 +2724,7 @@
@dataclass
class C:
c: int=field(default=D(), init=False)
- self.assertEqual(C.c.name, 'c')
+ self.assertEqual(C.c.name, 'cx')
self.assertEqual(C().c, 1)
def test_non_descriptor(self):
@@ -2733,12 +2733,41 @@
class D:
def __set_name__(self, owner, name):
- self.name = name
+ self.name = name + 'x'
@dataclass
class C:
c: int=field(default=D(), init=False)
- self.assertEqual(C.c.name, 'c')
+ self.assertEqual(C.c.name, 'cx')
+
+ def test_lookup_on_instance(self):
+ # See bpo-33175.
+ class D:
+ pass
+
+ d = D()
+ # Create an attribute on the instance, not type.
+ d.__set_name__ = Mock()
+
+ # Make sure d.__set_name__ is not called.
+ @dataclass
+ class C:
+ i: int=field(default=d, init=False)
+
+ self.assertEqual(d.__set_name__.call_count, 0)
+
+ def test_lookup_on_class(self):
+ # See bpo-33175.
+ class D:
+ pass
+ D.__set_name__ = Mock()
+
+ # Make sure D.__set_name__ is called.
+ @dataclass
+ class C:
+ i: int=field(default=D(), init=False)
+
+ self.assertEqual(D.__set_name__.call_count, 1)
if __name__ == '__main__':