[Python-ideas] Delay evaluation of annotations

[Nick Coghlan]

On 27 September 2016 at 17:29, Neil Girdhar <mistersheik at gmail.com> wrote:
> On Friday, September 23, 2016 at 2:23:58 AM UTC-4, Nick Coghlan wrote:
>> The difference between that and the "methods referring to the class
>> they're defined in" case is that it's likely to be pretty normal to
>> want to do the latter, so it may prove worthwhile to provide a cleaner
>> standard spelling for it. The counter-argument is the general
>> circularity one above: do you *really* need instances of the
>> particular class being defined? Or is there a more permissive
>> interface based type signature you could specify instead? Or perhaps
>> no type signature at all, and let ducktyping sort it out implicitly at
>> runtime?
>
> I agree that circularity should in general be avoided, but it's not always
> possible or elegant to do that.  Sometimes you really need two classes to
> refer to each other. In that case, why not expose your placeholder idea to
> the user via a library? You have one function that generates placeholder
> singletons (generate_placeholder()), and another function to walks a class
> object and replaces a placeholder with a given value
> (replace_placeholder(placeholder, cls, value)).

Because the general case is already covered by using a quoted string
instead of a name reference. "I don't like using strings to denote
delayed evaluation" isn't a compelling argument, which is why
alternative ideas have to offer some other significant benefit, or
else be incredibly simple both to implement and to explain.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia