[mypyc] Support deleting attributes in __setattr__ wrapper #19997
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JukkaL
reviewed
Oct 6, 2025
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| # Doesn't work because there's no __delattr__. | ||
| with assertRaises(AttributeError): | ||
| del i.four |
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Maybe mypy could catch this? If four is not a declared attribute and there is no __delattr__, this is expected to fail. If you agree, can you create a mypy issue about this (unless one already exists)?
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I don't think mypy can catch this because this is a quirk of native classes. For interpreted classes that define __setattr__ deleting an attribute works without __delattr__ because it just removes it from __dict__. It's only native classes that might need an explicit __delattr__. So I think the error would be specific to mypyc.
JukkaL
approved these changes
Oct 6, 2025
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The
__setattr__wrapper that mypyc generates needs to handle deleting attributes as well becausedelstatements go through the sametp_setattropointer but with the value argument set toNULL.The wrapper calls
__delattr__in this case if it's overridden in the native class (or its parent). Handling of dynamic attributes is different without__dict__which makes a custom__delattr__required if the dynamic attributes are stored in a custom dictionary.If
__delattr__is not overridden it calls the implementation ofobject.__delattr__which results inAttributeErrorbecause there's no__dict__.If it's defined without
__setattr__, mypyc reports an error. It's possible to support just__delattr__but since it shares a slot with__setattr__, the wrapper generation would be more complicated. It seems like an unlikely use case to only need__delattr__so I think it makes sense to leave it for later.