On Sun, Jan 6, 2013 at 9:47 PM, Nick Coghlan <ncoghlan@gmail.com> wrote:
On Mon, Jan 7, 2013 at 2:24 AM, Guido van Rossum <guido@python.org> wrote:
On Sunday, January 6, 2013, Nick Coghlan wrote:
On Sun, Jan 6, 2013 at 8:20 PM, Laurens Van Houtven <_@lvh.cc> wrote:
Hi Nick,
When you say "high latency" (in __exit__), what does "high" mean? Is that order of magnitude what __exit__ usually means now, or network IO included?
(Use case: distributed locking and remotely stored locks: it doesn't take a long time on network scales, but it can take a long time on CPU scales.)
The status quo can only be made to work for in-memory locks. If the release step involves network access, then it's closer to the "database transaction" use case, because the __exit__ method may need to block.
But you don't need to wait for the release. You can do that asynchronously.
Ah, true, I hadn't thought of that. So yes, any case where the __exit__ method can be "fire-and-forget" is also straightforward to implement with just PEP 3156. That takes us back to things like database transactions being the only ones where
And 'yielding' wouldn't do anything about this, would it?
Also, have you given the implementation of your 'yielding' proposal any thought yet?
Not in depth. Off the top of my head, I'd suggest: - make "yielding" a new kind of node in the grammar (so you can't write "yielding expr" in arbitrary locations, but only in those that are marked as allowing it) - flag for loops and with statements as accepting these nodes as iterables and context managers respectively - create a new Yielding AST node (with a single Expr node as the child) - emit different bytecode in the affected compound statements based on whether the relevant subnode is an ordinary expression (thus invoking the special methods as "obj.__method__()") or a yielding one (thus invoking the special methods as "yield from obj.__method__()").
I'm not seeing any obvious holes in that strategy, but I haven't looked closely at the compiler code in a while, so there may be limitations I haven't accounted for.
So would 'yielding' insert the equivalent of 'yield from' or the equivalent of 'yield' in the code? -- --Guido van Rossum (python.org/~guido)