Description
Structs that were defined with custom metaclass (subclass of msgspec.StructMeta) can't be subclassed with msgspec.defstruct. (msgspec 0.20.0)
Following code:
import msgspec
class _FooStructMeta(msgspec.StructMeta):
def __new__(mcls, name, bases, namespace, **struct_config):
return super().__new__(mcls, name, bases, namespace, **struct_config)
class FooStruct(msgspec.Struct, metaclass=_FooStructMeta):
pass
BarStruct = msgspec.defstruct(name="BarStruct", fields=[("id", int)], bases=(FooStruct,))Raises this error:
Traceback (most recent call last):
File "/home/jirka642/.config/JetBrains/PyCharm2025.3/scratches/scratch_1.py", line 13, in <module>
BarStruct = msgspec.defstruct(name="BarStruct", fields=[("id", int)], bases=(FooStruct,))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jirka642/.config/JetBrains/PyCharm2025.3/scratches/scratch_1.py", line 6, in __new__
return super().__new__(mcls, name, bases, namespace, **struct_config)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: Struct types cannot define __slots__
I have been able to hotfix it by running namespace.pop("__slots__", None) in the metaclass, but I'm not sure if that is safe.
Description
Structs that were defined with custom metaclass (subclass of
msgspec.StructMeta) can't be subclassed withmsgspec.defstruct. (msgspec 0.20.0)Following code:
Raises this error:
I have been able to hotfix it by running
namespace.pop("__slots__", None)in the metaclass, but I'm not sure if that is safe.