On Wed, 9 Dec 2020 at 09:27, Mathew Elman <mathew.elman@ocado.com> wrote:
I agree that if you are using them as iterables, then the type is usually not important because you are treating their type as just iter-able. The lazy iterable would more or less just be the same as passing in `iter(sequence)`.
This is for other use cases where the use of the object is specific to the type, e.g. a case where in the outer scope you construct a list and mutate it but when it is passed to an inner scope, you want to enforce that it can be accessed but not mutated. Likewise if lazy built in types were implemented in python then getting a slice of a sequence could also be done lazily, whereas my understanding at the moment is that it has to create a whole new sequence.
If you need this for annotations/typing alone, can't you just use `typing.cast` in the inner scope? (or before calling it for that matter) Anyway, mypy at least wil error if you annotate the inner scope as a "Sequence" (in contrast with MutableSequence), and will error if you try to change the Sequence - and it stlll remain compatible with incoming "MutableSequences". For the cases it does not cover, there is still "cast" - and it feels _a lot_ simpler than having actual runtime lazy objetcs as primitives in the language.
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