Hello,
There’s been discussion on the typing of homogeneous tuples of fixed and variable length (e.g. here or here or PEP-484), for example
tuple[int, str] # Two-tuple of an integer and string.
tuple[int, ...] # Tuple of integers of variable length.
tuple # Synonymous with tuple[Any, ...]
In the following I’d like to discuss nonhomogeneous tuples of variable length, for which I would like to express some type constraints.
For context: the question arose while I played around with SQLAlchemy’s declarative table configuration (docs) which states:
Keyword arguments can be specified with the above form [a tuple] by specifying the last argument as a dictionary
meaning that we have a tuple of some items, the last of which is a dictionary. This can’t currently be expressed, AFAIK.
So I started wondering if we could take an approach that’s somewhat similar to Python’s iterable unpacking of expression lists (docs), and interpret the ellipsis ... similarly to the *. For example
tuple[..., dict]
where the initial ellipsis ... would mean “zero or more items of type Any” with the last item being a dict. If we stick with that interpretation of the ellipsis then we’d also be able to express more elaborate shapes like
# Must contain an integer, then string, then anything, ending in a list.
tuple[int, str, ..., list]
Whould this make sense? Would this be something useful to add?
Cheers,
Jens
