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Re: Python Sanity Proposal: Type Hinting Solution

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Steven D'Aprano <steve+comp.lang.python@pearwood.info>:

> Marko Rauhamaa wrote:
>
>>    def weekday(day):
>>        assert isinstance(day, int) and 0 <= day <= 6
>>        ...
>
> [...]
>
> Requiring the type-checker to parse and understand arbitrarily complex
> assertions would require the type-checker to be as complex as Python
> itself:

The static type checker / optimizer would of course be limited to a set
of known fixed expression patterns. More complex expressions would
simply be ignored by it.

Moreover, the type checker would probably operate in a compile-time
environment where you assume "isinstance" and "int" retain their usual
meanings. 

Scheme already employs somewhat analogous dirty tricks like that in its
macro preprocessing.

> Assertions also have the problem that they execute arbitrarily complex
> code at runtime.

Assertions don't *have* to execute anything, anywhere, any time. The
static analysis can decide when executing assertions is worth the
trouble. All of the above can also be done JIT.

> Lastly, this use of assertions clashes with "best practice" for
> assertions. Since assertions may be disabled, you should not use them
> for testing user-supplied arguments. So that means you have to write:
>
> def func(arg):
>     assert isinstance(arg, int)  # satisfy the type checker
>     if isinstance(arg, int):  # support times when assert is disabled
>         ...

I think that's a silly argument. You never second-guess assertions.

> This doesn't apply to annotations:
>
> def func(arg:int):
>     # since this is a public function, not private, we cannot assume the
>     # caller will run the type-checker
>     if isinstance(arg, int):
>         ...

I think that usage is plainly bad style as well. Reminds me of the old
adage:

   Dad is always right, and even when he isn't, he's never wrong.


Marko

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Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-22 17:15 -0800
  Re: Python Sanity Proposal: Type Hinting Solution MRAB <python@mrabarnett.plus.com> - 2015-01-23 03:22 +0000
  Re: Python Sanity Proposal: Type Hinting Solution Terry Reedy <tjreedy@udel.edu> - 2015-01-22 22:22 -0500
    Re: Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-23 11:23 -0800
      Re: Python Sanity Proposal: Type Hinting Solution Christian Gollwitzer <auriocus@gmx.de> - 2015-01-24 22:14 +0100
  Re: Python Sanity Proposal: Type Hinting Solution Rustom Mody <rustompmody@gmail.com> - 2015-01-22 19:23 -0800
    Re: Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-23 11:36 -0800
  Re: Python Sanity Proposal: Type Hinting Solution Chris Angelico <rosuav@gmail.com> - 2015-01-23 14:59 +1100
    Re: Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-23 11:48 -0800
      Re: Python Sanity Proposal: Type Hinting Solution Chris Angelico <rosuav@gmail.com> - 2015-01-24 06:59 +1100
        Re: Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-23 12:59 -0800
      Re: Python Sanity Proposal: Type Hinting Solution Mario Figueiredo <marfig@gmail.com> - 2015-01-23 22:02 +0100
        Re: Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-23 13:59 -0800
          Re: Python Sanity Proposal: Type Hinting Solution Mario Figueiredo <marfig@gmail.com> - 2015-01-23 23:42 +0100
            Re: Python Sanity Proposal: Type Hinting Solution Mario Figueiredo <marfig@gmail.com> - 2015-01-23 23:45 +0100
              Re: Python Sanity Proposal: Type Hinting Solution sohcahtoa82@gmail.com - 2015-01-23 14:52 -0800
                Re: Python Sanity Proposal: Type Hinting Solution Mario Figueiredo <marfig@gmail.com> - 2015-01-24 00:14 +0100
              Re: Python Sanity Proposal: Type Hinting Solution Marko Rauhamaa <marko@pacujo.net> - 2015-01-24 01:52 +0200
                Re: Python Sanity Proposal: Type Hinting Solution Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-24 16:29 +1100
                Re: Python Sanity Proposal: Type Hinting Solution Chris Angelico <rosuav@gmail.com> - 2015-01-24 16:38 +1100
                Re: Python Sanity Proposal: Type Hinting Solution Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-24 17:36 +1100
                Re: Python Sanity Proposal: Type Hinting Solution Chris Angelico <rosuav@gmail.com> - 2015-01-24 17:47 +1100
                Re: Python Sanity Proposal: Type Hinting Solution Marko Rauhamaa <marko@pacujo.net> - 2015-01-24 11:27 +0200
            Re: Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-23 15:39 -0800
            Re: Python Sanity Proposal: Type Hinting Solution Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-25 00:29 +1100
              Re: Python Sanity Proposal: Type Hinting Solution Mario Figueiredo <marfig@gmail.com> - 2015-01-24 15:09 +0100
                Re: Python Sanity Proposal: Type Hinting Solution Mario Figueiredo <marfig@gmail.com> - 2015-01-24 15:32 +0100
                Re: Python Sanity Proposal: Type Hinting Solution Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-25 03:05 +1100
                Re: Python Sanity Proposal: Type Hinting Solution Marco Buttu <marco.buttu@gmail.com> - 2015-01-24 15:25 +0100
              Re: Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-24 08:41 -0800
                Re: Python Sanity Proposal: Type Hinting Solution Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-25 04:26 +1100
                Re: Python Sanity Proposal: Type Hinting Solution Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-01-24 17:36 +0000
                Re: Python Sanity Proposal: Type Hinting Solution Paul Rubin <no.email@nospam.invalid> - 2015-01-24 09:37 -0800
                Re: Python Sanity Proposal: Type Hinting Solution Chris Angelico <rosuav@gmail.com> - 2015-01-25 06:59 +1100
  Re: Python Sanity Proposal: Type Hinting Solution Terry Reedy <tjreedy@udel.edu> - 2015-01-23 00:03 -0500
    Re: Python Sanity Proposal: Type Hinting Solution Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-23 16:59 +1100
      Re: Python Sanity Proposal: Type Hinting Solution "Fetchinson ." <fetchinson@googlemail.com> - 2015-01-23 14:23 +0100
        Re: Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-23 12:21 -0800
          Re: Python Sanity Proposal: Type Hinting Solution Mario Figueiredo <marfig@gmail.com> - 2015-01-23 22:12 +0100
            Re: Python Sanity Proposal: Type Hinting Solution Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-23 14:26 -0800
        Re: Python Sanity Proposal: Type Hinting Solution Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-24 17:21 +1100
          Re: Python Sanity Proposal: Type Hinting Solution Tim Chase <python.list@tim.thechases.com> - 2015-01-24 06:47 -0600
            Re: Python Sanity Proposal: Type Hinting Solution Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-25 00:40 +1100
              Re: Python Sanity Proposal: Type Hinting Solution Roy Smith <roy@panix.com> - 2015-01-24 09:06 -0500
          Re: Python Sanity Proposal: Type Hinting Solution "Fetchinson ." <fetchinson@googlemail.com> - 2015-01-24 22:01 +0100
      Re: Python Sanity Proposal: Type Hinting Solution Chris Angelico <rosuav@gmail.com> - 2015-01-24 04:11 +1100
      Re: Python Sanity Proposal: Type Hinting Solution "Fetchinson ." <fetchinson@googlemail.com> - 2015-01-23 22:07 +0100
  Re: Python Sanity Proposal: Type Hinting Solution Chris Angelico <rosuav@gmail.com> - 2015-01-23 16:31 +1100

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