On Mon, Dec 28, 2020 at 7:45 PM Anton Abrosimov <[email protected]> wrote:
>
> Steven D'Aprano wrote:
> > Why do you want something that isn't a mapping to be usable with mapping
> > unpacking?
>
> I think mapping is not `abc.Mapping` class only.
>
> What about:
> `Iterator[Tuple[str, int]]`
>
> ```
> @dataclass
> class MyMap:
> x: int
> y: int
> ```
>
> Is this "mapping"?
> In Python I can use `/` as path separator: `pathlib.Path.cwd() / 'my_dir'`. I
> can control the behavior of my class.
> But I only have one way to unpack the object. Not a perfect way. `dict.update
> ()` gives more freedom.
>
> Steven D'Aprano wrote:
> > Does it really hurt you to provide mapping methods when you get them
> > for free? Just inherit from Mapping.
>
> ```
> # first.py:
> @dataclass
> class Point2D(Mapping):
>
> # second.py
> @dataclass
> class Point3D(Point2D):
> ```
>
> Now I have to think about unnecessary public methods.
Allow me to rephrase what I *think* you're arguing here, and you can
tell me if I'm close to the mark.
Given an object of a custom class C, you can make it usable as "x, y,
z = C()" or "f(*C())" or anything else by defining __iter__, and in
all ways that object will be iterable, unpackable, etc.
Given the same object, how can you ensure that it can be used as
"f(**C())"? What about in "{}.update(C())"? Or "dict(C())"? Is there a
single well-defined protocol that allows you to make your object
usable in all mapping-like contexts?
If that's not what your point is, ignore this post :)
ChrisA
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