On 24 March 2018 at 09:49, Chris Angelico email@example.com wrote:
Of course we don't want to necessarily impose unreasonable performance and maintence costs on any implementation. But surely performance cost is a quality of implementation issue. It ought to be a matter of trade-offs: is the benefit sufficient to make up for the cost?
I don't see where this comes in. Let's say that Jython can't implement this feature without a 10% slowdown in run-time performance even if these subscopes aren't used. What are you saying the PEP should say? That it's okay for this feature to hurt performance by 10%? Then it should be rightly rejected. Or that Jython is allowed to ignore this feature? Or what?
I think the PEP should confirm that there's not expected to be a showstopper performance cost in implementing this feature in other Python implementations. That doesn't have to be a big deal - reaching out to the Jython, PyPy, Cython etc implementors and asking them for a quick sanity check that this doesn't impose unmanageable overheads should be sufficient. No need to make this too dogmatic.