[Python-Dev] Is static typing still optional? (original) (raw)

Stephan Hoyer shoyer at gmail.com
Fri Dec 22 13:10:51 EST 2017

On Thu, Dec 21, 2017 at 6:39 AM Ivan Levkivskyi <levkivskyi at gmail.com> wrote:

For me, the three options for "don't care" have a bit different meaning:

* typing.Any: this class is supposed to be used with static type checkers, but this field is too dynamic * ... (ellipsis): this class may or may not be used with static type checkers, use the inferred type in the latter case * "field docstring": this class should not be used with static type checkers Assuming this, the second option would be the "real" "don't care". If this makes sense, then we can go the way proposed in https://github.com/python/typing/issues/276 and make ellipsis semantics "official" in PEP 484. (pending Guido's approval)

I am a little nervous about using "..." for inferred types, because it could potentially cause confusion with other uses of ellipsis in typing.

Ellipsis already has a special meaning for Tuple, so an annotation like MyClass[int, ...] could mean either a tuple subclass with integer elements or a two argument generic type where the second type is inferred. Actually, it's ambiguous even for Tuple.

Ellipsis could also make a lot of sense for typing multi-dimensional arrays similar to how it's used in indexing to denote "any number of dimensions." Again, the semantics for "..." might defer from "an inferred size."

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