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

[Guido van Rossum]

On Wed, Aug 13, 2014 at 5:53 PM, Haoyi Li <haoyi.sg at gmail.com> wrote:

> > Both solutions have merit, but the idea of some implementations of the
> type checker having covariance and some contravariance is fairly
> disturbing.
>
> Why can't we have both? That's the only way to properly type things, since
> immutable-get-style APIs are always going to be convariant, set-only style
> APIs (e.g. a function that takes 1 arg and returns None) are going to be
> contravariant and mutable get-set APIs (like most python collections)
> should really be invariant.
>

That makes sense. Can you put something in the mypy tracker about this? (Or
send a pull request. :-)

-- 
--Guido van Rossum (python.org/~guido)
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