[Python-ideas] Proposal: Use mypy syntax for function annotations

[Terry Reedy]

On 8/25/2014 11:12 AM, Guido van Rossum wrote:
> On Sun, Aug 24, 2014 at 11:18 PM, Terry Reedy

>     I believe co-existence is possible, but the details will depend on
>     the form type hints take. First, other annotations should be easily
>     distinguished from type hints. Second, other annotations that would
>     interfere with the runtime use of __annotations__ should be pulled
>     out by a decorator and possibly moved to another attribute specific
>     to the decorator (such as '_deco_name').
>
>
> What exactly do you mean by "other annotations that would interfere with
> the runtime use of __annotations__"?

I am referring to the current stdlib runtime use of .__annotations__ 
directly by inspect.getfullargspec and now inspect.signature and 
indirectly by Idle calltips.

def f(n:[int, 'random non-type info'])->(int, 'more non-type info'): pass
import inspect as ip
print(ip.formatargspec(*ip.getfullargspec(f)))
print(str(ip.signature(f)))

(n: [<class 'int'>, 'random non-type info']) -> (<class 'int'>, 'more 
non-type info')
(n:[<class 'int'>, 'random non-type info']) -> (<class 'int'>, 'more 
non-type info')

(Idle currently displays the first, will change to the second. The 
display difference is more pronounced (now, at least) for C functions 
with .__text_signature__ from Argument Clinic.)

To me, 'argument specification' and especially 'signature' imply 
arguments names and types, but not other stuff. Certainly, name and type 
is all that is wanted for a tip on how to write a call.  Extra stuff 
would typically be noise in this context -- especially for beginners.

> I can only assume that you are thinking of a situation where you are
> introspecting some function/method of unknown origin and you are trying
> to see if it has any annotations, in which case you are going to use
> them for a locally-defined use (e.g. generate an HTML form -- contrived
> example).
>
> It sounds as if you are worried about being passed a function that in
> the past would not have any annotations (so you would just generate a
> default form based on the argument names) but which now has been
> annotated by a zealous programmer with type hints. And you are worried
> that those type hints will confuse (perhaps crash) the form-generation code.

I am worried about annotations other than type hints. Compact type 
hints, especially for type-opaque parameter names, should improve the 
usefulness of call tips. Extra noise detracts.

If type hints were standardized so as to be easily recognizable, 
.signature could be given an option to ignore anything else.

-- 
Terry Jan Reedy