I would like to add another view of this feature might be very useful for cleaning up existing code bases: Just have a look at https://pypi.org/project/xfork/ and specifically I would like to point you to the following lines https://github.com/srkunze/fork/blob/afecde0/fork.py#L216 till #419. As you can see these whooping 203 lines are for the sake of implementing a delaying proxy class (of a 520 lines project). If this feature gets added, the almost the whole implementation could *shrink to a mere line* of (I hope): delayed: future.result() That would be awesome! Btw. adding parameters to 'delayed' like lambda would also be useful. [I gather that delayed is a mere placeholder for now.] On 18.02.2017 12:10, Nathaniel Smith wrote:
On Fri, Feb 17, 2017 at 9:34 PM, David Mertz <mertz@gnosis.cx> wrote:
On Fri, Feb 17, 2017 at 6:20 PM, Nathaniel Smith <njs@pobox.com> wrote:
value = delayed: some_dict.get("whatever") if value is None: ...
I.e., the question is, how does 'is' work on delayed objects? I guess it has to force the promise and walk the proxy chain in each input and then do an 'is' on the base objects?
You've explained the semantics exactly. That's not confusing at all. Okay... so what if I want to check if two objects refer to the same delayed computation? I guess you can say that's just not supported, but that's *extraordinarily weird* for Python.
It's new to Python yes, but it's not weird. You already can implement such proxies today as I've demonstrated.
And at the implementation level... so you just added two type checks and two branches to every 'is' call; this seems concerning. And now 'is' can raise an error, which it never could before. You also AFAICT have to modify every single C extension function to check for and handle these things, which is probably impossible even if the overhead of all the checks is acceptable, which isn't obvious. I'm just not seeing how this could be implemented.
I don't share your concerns here. What you describe is the nature of *delayed*. It's not only applicable to 'is' but to all operations which evaluate delayed objects. My point of view from the other side: me and other people need delayed proxies, so they implement them, and all of us make the same mistakes over and over gain. Cheers, Sven