26.12.20 13:23, Anton Abrosimov пише:
I am trying to release comfortable dataclass unpacking using `**` operator. Now I have 5 different ways to do it. But not a single good one. Confused by the implementation of the unpacking operator.
So when I try to unpack any custom class, I get the error:
`type object argument after ** must be a mapping, not MyClass`
Ok, nothing special. I need to use `collections.abc.Mapping` right? Now I need to implement: `__getitem__`, `__iter__`, `__len__`. Not a problem. But additionally I get: `keys`, `items`, `values`. Hey, I don't need them. I don't need the full mapping functionality. I only need the double asterisk to work.
Right, we have a duck typing! We throw out `abc.Mapping`. What do we need to implement? It's `__getitem__` and `keys`. Wtf `keys`?
I am looking at Python Data model: https://docs.python.org/3/reference/datamodel.html There many operators, and they depend on special double underscore methods. Hmm, I don't see unpack operators there, it's strange. But why it's `keys`? Because the historical is `dict`? I think a dependency on `__iter__` is more preferable and expectable over a userspace named `keys`. Actually, `items()` is more predictable.
See thread "Add __keys__ or __items__ protocol". https://mail.python.org/archives/list/python-ideas@python.org/thread/A3CK7Y2...