bpo-33141: Have dataclasses.Field pass through __set_name__ to any default argument. (GH-6260)
This is part of PEP 487 and the descriptor protocol.
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 @@
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',