Mailman 3 December 2019 - Typing-sig

Explicit Type Aliases
by Shannon Zhu 17 Aug '22

17 Aug '22

Hi everyone, I’d like to continue the discussion from our last typing summit on explicit type aliases. A quick summary of the current state and the proposal -- Current state: ``` from typing import List x = List[int] # considered a type alias y : Type[List[int]] = List[int] # considered an expression z : Any # considered a type alias z : x = [] # fine z : y = [] # invalid type error ``` Proposal (with explicit aliases): ``` from typing import List, TypeAlias x = TypeAlias[List[int]] # considered a type alias y = List[int] # considered an expression z : Any # considered an expression z = TypeAlias[Any] # considered a type alias reveal_type(x) # Type[List[int]] reveal_type(y) # Any (return type of __getitem__) z : x = [] # fine z : y = [] # invalid type error ``` Some of the benefits we’re hoping to gain from explicit type aliases: * Clearly distinguish between an unannotated global assignment and a type alias, especially when parsing forward-referencing string annotations. * Avoid the confusing case of type aliases in which some part of the type is invalid or undefined. This would facilitate warnings on invalid types at the alias definition rather than later on when the alias is used. * Make valid and invalid types more intuitive to Python programmers by shifting from delineation of non-aliases with a meta annotation toward delineation of aliases with `TypeAlias`. * Remove special treatment of values annotated as `Any`, which currently break all type aliasing rules. This will also allow us to clean up some of the distinctions we maintain between unannotated values and explicit Anys. Note: We also considered denoting the alias as an annotation (e.g. `x: TypeAlias = int`) as an alternative to the syntax above. I’m interested to hear your thoughts and suggestions on making type aliasing explicit going forward – we’d like to start implementing a version of this in Pyre soon! Shannon

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Bay Area Typing Meetup 9/20
by Dominik Gabi 01 Jun '20

01 Jun '20

Jukka and Ivan will be visiting the Bay Area in September and we'd like to organize another meetup. Here are the proposed (tentative) logistics: Date: Friday, Sept. 20 Time: 1pm - 5pm Location: Facebook in Menlo Park (building and room TBD) So far Ivan, Jukka, Guido, Rebecca, Martin (?), and myself have committed to attending. I'm also volunteering the rest of the Pyre team. Please let us know in advance if you plan on attending so that we can book an adequately sized room. Also now's the time to think about topics to discuss or presentations you want to give. – Dominik

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PEP 593: Flexible function and variable annotations
by Till 03 Mar '20

03 Mar '20

Hi, We've just landed pep-593 (https://www.python.org/dev/peps/pep-0593/); it proposes adding support to embed metadata inside type annotations. I'm looking forward to hearing people's opinion. Best, Till

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PEP 612: Parameter Specification Variables
by Mark Mendoza 21 Feb '20

21 Feb '20

Hi All, I want to announce the submission of a new typing PEP, for ParameterSpecifications (https://github.com/python/peps/pull/1259). We discussed this concept at the last typing summit (presentation can be found here https://github.com/facebook/pyre-check/blob/master/docs/Variadic_Type_Varia…), and there seemed to be general consensus on the utility of this idea, and the appropriateness of the particular solution. One note that I know there was some disagreement on was the name for the feature itself, with some folks preferring ArgSpec. I wrote up a brief note in the PEP itself why we're not as big fans of that name, but I'd love to hear all of your opinions on this issue, as well as on anything else in the PEP. Best, Mark Mendoza

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Wintel Engineer jobs
by ravi fieldengineer 26 Jan '20

26 Jan '20

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Re: PEP 612: Parameter Specification Variables
by Andrew Svetlov 03 Jan '20

03 Jan '20

I personally prefer shorter to type names, so ArgsSpec looks better in my eyes. Concatenate and ListVariadic seems satisfactory for positional arguments. You know, Python supports positional-only, keyword-only, *args and **kwargs also. Could ArgsSpec (or ParameterSpecifications) be extended to explicitly provide these kinds of parameters explicitly? Another thing is the default argument. The exact value of the default is not significant for typing but a flag of the default value presence is important. Can ArgsSpec provide this information? -- Thanks, Andrew Svetlov

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