[Python-Dev] Type hints -- a mediocre programmer's reaction

[Chris Angelico]

On Tue, Apr 21, 2015 at 6:58 PM, Cory Benfield <cory at lukasa.co.uk> wrote:
> On 21 April 2015 at 01:45, Chris Angelico <rosuav at gmail.com> wrote:
>> When you're writing a library, it can be a great help to provide type
>> annotations, because every application that uses your library can
>> benefit.
>
> It can be a great help to whom? Not to me (the library author),
> because I can't use them in my library code, because I have to support
> 2.7. That's by no means a bad thing (after all, most libraries are
> written to help others), but I found it really unclear who was being
> advantaged here.

Mainly application users get the benefit, I expect. But I may be wrong.

> ... That's got *nothing* on the type of the `files`
> argument, which is the most incredibly polymorphic argument I've ever
> seen: the best I can work out it would be:
>
> Optional[
>     Union[
>         Mapping[
>             basestring,
>             Union[
>                 Tuple[basestring, Optional[Union[basestring, file]]],
>                 Tuple[basestring, Optional[Union[basestring, file]],
> Optional[basestring]],
>                 Tuple[basestring, Optional[Union[basestring, file]],
> Optional[basestring], Optional[Headers]]
>             ]
>         ],
>         Iterable[
>             Tuple[
>                 basestring,
>                 Union[
>                     Tuple[basestring, Optional[Union[basestring, file]]],
>                     Tuple[basestring, Optional[Union[basestring,
> file]], Optional[basestring]],
>                     Tuple[basestring, Optional[Union[basestring,
> file]], Optional[basestring], Optional[Headers]]
>             ]
>         ]
>     ]
> ]

At this point, you may want to just stop caring about the exact type.
Part of the point of gradual typing is that you can short-cut a lot of
this. And quite frankly, this isn't really helping anything. Just skip
it and say that it's Union[Mapping, Iterable, None].

ChrisA