Akuli <akuviljane...@gmail.com> added the comment:
> I also think that keeping a status quo (ignoring the mapping attribute in
> typing) is the lesser evil.
Can you clarify this? There are several things that typing could do, and I
don't know which option you are referring to. I listed most of them below, and
I'd like to know which exactly of them "is the lesser evil".
If we literally ignore the attribute, any usage of `.mapping` will be an error,
which basically makes the whole `.mapping` feature useless for statically typed
code. It also wouldn't appear in IDE autocompletions.
If we add it to `KeysView` and `ValuesView`, library authors will end up using
`.mapping` with arguments annotated as `Mapping` or `MutableMapping`, not
realizing it is purely a dict thing, not required from an arbitrary mapping
object.
If we keep `.mapping` in dict but not anywhere else, as described already, it
becomes difficult to override .keys() and .values() in a dict subclass. You
can't just return a KeysView or a ValuesView. If that was allowed, how should
people annotate code that uses `.mapping`? You can't annotate with `dict`,
because that also allows subclasses of dict, which might not have a `.mapping`
attribute.
Yet another option would be to expose `dict_keys` and `dict_values` somewhere
where they don't actually exist at runtime. This leads to code like this:
from typing import Any, TYPE_CHECKING
if TYPE_CHECKING:
# A lie for type checkers to work.
from something_that_doesnt_exist_at_runtime import dict_keys, dict_values
else:
# Runtime doesn't check type annotations anyway.
dict_keys = Any
dict_values = Any
While this works, it isn't very pretty.
----------
nosy: +Akuli
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<https://bugs.python.org/issue46399>
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