Contradicting requirements in collections.abc.Sequence docs and typing information

[502E532E]

Documentation

The collections.abc.Sequence docs state that __getitem__ needs to be implemented, and link to some general __getitem__ docs. It states

For sequence types, the accepted keys should be integers. Optionally, they may support slice objects as well.

But the corresponding typing information requires slice support.

To resolve this, either the docs or the typing information should be adapted.

Related

#120802 (general __getitem__ docs improvements)
My corresponding question and answer on Stackoverflow

[rhettinger]

Yes, the two disagree on this point, but there is nothing that can be done about it. It is just a fact of life.

The ABCs are intentionally minimal requirements for what it means to be a Sequence. Some sequences in the real world don't have slicing support, either because it isn't needed, because it doesn't make sense for use case, or because it is difficult to implement slicing support.

In contrast, TypeShed tries to adapt to what many concrete sequences actually do which is to have slice support. If it didn't, then slices on lists, tuples, and strings would be flagged as invalid.

Guido has commented before that the needs to typing sometimes conflict with practical realities where existing tools don't fit neatly into the boxes that were designed after the fact.