diff options
| -rw-r--r-- | Lib/dataclasses.py | 14 | ||||
| -rwxr-xr-x | Lib/test/test_dataclasses.py | 42 | ||||
| -rw-r--r-- | Misc/NEWS.d/next/Library/2018-03-26-12-33-13.bpo-33141.23wlxf.rst | 2 |
3 files changed, 58 insertions, 0 deletions
diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py index 8ccc4c8..8c197fe 100644 --- a/Lib/dataclasses.py +++ b/Lib/dataclasses.py @@ -240,6 +240,20 @@ class Field: f'metadata={self.metadata}' ')') + # This is used to support the PEP 487 __set_name__ protocol in the + # case where we're using a field that contains a descriptor as a + # defaul value. For details on __set_name__, see + # https://www.python.org/dev/peps/pep-0487/#implementation-details. + # Note that in _process_class, this Field object is overwritten with + # 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) + if func: + # There is a __set_name__ method on the descriptor, + # call it. + func(owner, name) + class _DataclassParams: __slots__ = ('init', diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py index f7f132c..2745eaf 100755 --- a/Lib/test/test_dataclasses.py +++ b/Lib/test/test_dataclasses.py @@ -2698,6 +2698,48 @@ class TestSlots(unittest.TestCase): # We can add a new field to the derived instance. d.z = 10 +class TestDescriptors(unittest.TestCase): + def test_set_name(self): + # See bpo-33141. + + # Create a descriptor. + class D: + def __set_name__(self, owner, name): + self.name = name + def __get__(self, instance, owner): + if instance is not None: + return 1 + return self + + # This is the case of just normal descriptor behavior, no + # dataclass code is involved in initializing the descriptor. + @dataclass + class C: + c: int=D() + self.assertEqual(C.c.name, 'c') + + # Now test with a default value and init=False, which is the + # only time this is really meaningful. If not using + # init=False, then the descriptor will be overwritten, anyway. + @dataclass + class C: + c: int=field(default=D(), init=False) + self.assertEqual(C.c.name, 'c') + self.assertEqual(C().c, 1) + + def test_non_descriptor(self): + # PEP 487 says __set_name__ should work on non-descriptors. + # Create a descriptor. + + class D: + def __set_name__(self, owner, name): + self.name = name + + @dataclass + class C: + c: int=field(default=D(), init=False) + self.assertEqual(C.c.name, 'c') + if __name__ == '__main__': unittest.main() diff --git a/Misc/NEWS.d/next/Library/2018-03-26-12-33-13.bpo-33141.23wlxf.rst b/Misc/NEWS.d/next/Library/2018-03-26-12-33-13.bpo-33141.23wlxf.rst new file mode 100644 index 0000000..1d49c08 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2018-03-26-12-33-13.bpo-33141.23wlxf.rst @@ -0,0 +1,2 @@ +Have Field objects pass through __set_name__ to their default values, if +they have their own __set_name__. |