[Typing-sig] Re: Cleaner Syntax (was Proposal: Literal types)

I don't really have a strong opinion on this, but I also agree with postponing the discussion, at least until "from __future__ import annotations" becomes more widespread and we have more design space to work with. Regarding the problem with type aliases: just to throw out some wild ideas, maybe we could add special syntax for type aliases to bring symmetry? Or look into adding some more general form of lazy evaluation? (I know python-ideas keeps bringing this idea up). Both ideas are probably overkill though -- the existing syntax is verbose, but not that bad IMO. On Tue, Nov 20, 2018 at 12:10 AM Sebastian Rittau wrote:

On 20.11.18 07:12, Michael Lee wrote:

...

During the typing meetup from a week or two ago, I mentioned that we (the mypy team) were planning on implementing Literal types and would have a draft of the proposed semantics ready soon. Well, here it is: https://github.com/Michael0x2a/peps/blob/literal-types/pep-9999.rst

I still think that we should eventually be able to use plain integers, True, False, and strings as shorthand for literals (in addition to the verbose Literal syntax). typing could be fixed for 3.8, strings are more difficult, but eventually a __future__ import could be introduced that disallows strings for quoting and allows it to be used as literal type.

[...snip...]

I agree this would be nice -- I also miss being able to write concise signatures a little. But due to the practical limitations discussed above, I don't think this kind of change is in scope of at least the literals PEP. -- Michael On Fri, Nov 23, 2018 at 3:37 AM Ivan Levkivskyi wrote:

On Tue, 20 Nov 2018 at 13:50, Sebastian Rittau wrote:

...

On 20.11.18 14:02, Ivan Levkivskyi wrote:

Finally, I also don't think the current syntax is optimal, I would rather have `Optional` -> `Opt`, `Callable` -> `Call`, plus maybe some _limited_ amount of special forms (for example only unions and tuples, because they are actually special). But this is still relatively minor and can be partially fixed by `from typing import Optional as Opt`, etc.

I think the big wins would be unions and optional types. These are the big two that are frequently used and often nested. Another one is the callable syntax, because it is easy to make mistakes, but since we have protocol based syntax now this is less important for complicated cases. Shorthanding lists, dicts, and other fundamental container types is more problematic, especially since Iterable, Sequence, Mapping, etc. should be used more frequently in argument types

The main problem with special syntax for unions is that annotations, type aliases, generic base classes etc. are evaluated at runtime, so for example we will need to add `type.__or__()`. I could imagine many people will be against this. Also we still don't have any evidence (not even a Twitter poll) that verbose syntax is a problem in adoption of typing in Python. I would propose to postpone this discussion, unless there is a strong evidence this is a problem.

-- Ivan

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