Add type for variable-length, uniform tuples

[gvanrossum]

See also https://github.com/JukkaL/typing/issues/6.

Some ideas:

• Tuple[int, ...]
• Sequence[int]

[gvanrossum]

It was pointed out on python-ideas that the language about this in the PEP is somewhat ambiguous, e.g. Tuple[t1, ..., t2] or Tuple[..., t1] should be clearly ruled out. (And the language currently clearly allows Tuple[t1, t2, ...] which I think should be ruled out too.)

[gvanrossum]

Also, does the empty tuple match Tuple[int, ...]?

I think it should; just like [] matches List[int].

[JukkaL]

I think an empty tuple should match Tuple[int, ...].

[gvanrossum]

This is decided and written up in the PEP: the syntax is Tuple[t1, ...] (the ... are a literal ellipsis).