On 2/6/20 4:23 PM, Serhiy Storchaka wrote: > It would create an exception of two rules: > > 1. Operators on subclasses of builtin classes do not depend on > overridden methods of arguments (except the corresponding dunder > method). `list.__add__` and `set.__or__` do not call copy() and > extend()/update(). You should override the corresponding dunder method > to change the behavior of the operator. > > 2. Operators do not depend on non-dunder methods. > > This looks to me as a direct violation of the principle "Special cases > aren't special enough to break the rules." > I may not fully understand the implications of #1, but I would think you could implement the semantics Brandt wants using only dunder methods and copy.copy (which itself dispatches to one of a number of dunder methods - __copy__, __reduce__, __setstate__, depending on which ones are defined - we could presumably avoid the `copy` import by partially porting that logic into `__or__`):
def __or__(self, other): new_value = copy.copy(self) for key in other.__keys__(): new_value.__setitem__(key, other.__getitem__(key)) return new_value Obviously the actual implementation would be in C and handle more edge cases and whatnot, but I think the desired semantics can all be achieved using only magic methods on the objects themselves (though we'd probably want to bypass all that stuff in favor of a "fast path" in the case of `dict` | `dict`). Best, Paul
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