[Python-ideas] Type Hinting Kick-off

[Ethan Furman]

On 12/21/2014 08:05 PM, Guido van Rossum wrote:
> On Sun, Dec 21, 2014 at 3:47 PM, Nick Coghlan <ncoghlan at gmail.com 
> <mailto:ncoghlan at gmail.com>> wrote:
>
>
>     On 22 December 2014 at 06:32, Andrew Svetlov
>     <andrew.svetlov at gmail.com <mailto:andrew.svetlov at gmail.com>> wrote:
>
>         Sorry, I want to ask again.
>         The proposal is for static checks only?
>         My expectations for processing annotations in runtime as-is
>         (just a
>         mark without any restrictions) will not changed?
>
>
>     Correct, there are no changes being proposed to the runtime
>     semantics of annotations. The type hinting proposal describes a
>     conventional use for them that will be of benefit to static type
>     checking systems and integrated development environments, but it
>     will be exactly that: a convention, not an enforced behaviour.
>
>
> Well... The elephant in the room is that *eventually* other uses of 
> annotations *may* be frowned upon, or may need to be marked by some 
> decorator. But I promise that in Python 3.5 your code will not break 
> -- it just might not be very useful to run a static checker like mypy 
> on it. (IIRC mypy used to only typecheck code that imports the 
> typing.py module, but this seems to have changed.)
>
> When we discussed this earlier this year, a few other uses of 
> annotations were brought up, and some have proposed that static type 
> annotations would need to be marked by a decorator. There is even a 
> proposed syntax that allows multiple annotations to coexist for the 
> same argument (a dict with fixed keys -- to me it looks pretty ugly 
> though).

What I ended up doing for my scription program was to move the 
annotations outside the  def, and store them in a different attribute, 
applied with a decorator:

@Command(
         file=('source file', ),
         dir=('target directory', ),
         options=('extra options', MULTI, ),
         )
def copy(file, dir, options):
     pass

copy.__scription__ --> {'file':..., 'dir':..., 'options':...}

--
~Ethan~
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