[Python-Dev] PEP 484 -- proposal to allow @overload in non-stub files (original) (raw)

Guido van Rossum guido at python.org
Thu Oct 22 13:51:15 EDT 2015

On Thu, Oct 22, 2015 at 2:21 AM, Gregory P. Smith <greg at krypto.org> wrote:

On Wed, Oct 21, 2015 at 6:51 PM Guido van Rossum <guido at python.org> wrote: Well the whole point is not to have to figure out how to implement that right now.

On Wed, Oct 21, 2015 at 6:45 PM, Random832 <random832 at fastmail.com> wrote:

Guido van Rossum <guido at python.org> writes: > The proposal is to allow this to be written as follows in > implementation (non-stub) modules: > > class Foo(Generic[T]): > @overload > def getitem(self, i: int) -> T: ... > @overload > def getitem(self, s: slice) -> Foo[T]: ... > def getitem(self, x): > > > The actual implementation must be last, so at run time it will > override the definition.

I think this could be fine. It is certainly readable. And, as is already possible in .pyi files, more accurately expressive than the Union which doesn't imply a parameter type to return value type relationship.

Right, which is how this got started.

What would it Foo.getitem.annotations contain in this situation? It'd unfortunately be an empty dict if implemented in the most trivial fashion rather than a dict containing your Unions... Do we care?

Initially it would indeed be {}. Once we have a true multi-dispatch PEP we can iterate, both on how to spell it (perhaps the final getitem needs an @overload as well) and on what happens in the annotations (or at least, what typing.get_type_hints() returns).

We could also wait for a multidispatch PEP to land -- but I'm worried that we'll be waiting past 3.6.

Then again I don't see how true multidispatch would be able to deal with the syntax proposed here -- you need some kind of decorator on the fallback implementation.

Note that it would also slow down module import time as the code for each of the earlier ... definitions with annotation structures and @overload decorator calls is executed, needlessly creating objects and structures that are immediately discarded upon each subsequent definition.

Yes, but I don't think this is going to make a noticeable difference.

-- --Guido van Rossum (python.org/~guido) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20151022/0fcfe095/attachment.html>

More information about the Python-Dev mailing list