[Python-ideas] Async API: some code to review

[Jakob Bowyer]

Sorry to chime in, but would this be a case where there could be the
syntax `yield to` ?

On Tue, Oct 30, 2012 at 10:12 AM, Laurens Van Houtven <_ at lvh.cc> wrote:
> Hi,
>
> I've been following the PEP380-related threads and I've reviewed this stuff,
> while trying to do the protocols/transports PEP, and trying to glue the two
> together.
>
> The biggest difference I can see is that protocols as they've been discussed
> are "pull": they get called when some data arrives. They don't know how much
> data there is; they just get told "here's some data". The obvious difference
> with the API in, eg:
>
> https://code.google.com/p/tulip/source/browse/sockets.py#56
>
> ... is that now I have to tell a socket to read n bytes, which "blocks" the
> coroutine, then I get some data.
>
> Now, there doesn't have to be an issue; you could simply say:
>
> data = yield from s.recv(4096) # that's the magic number usually right
> proto.data_received(4096)
>
> It seems a bit boilerplatey, but I suppose that eventually could be hidden
> away.
>
> But this style is pervasive, for example that's how reading by lines works:
>
> https://code.google.com/p/tulip/source/browse/echosvr.py#20
>
> While I'm not a big fan (I may be convinced if I see a protocol test that
> looks nice); I'm just wondering if there's any point in trying to write the
> pull-style protocols when this works quite differently.
>
> Additionally, I'm not sure if readline belongs on the socket. I understand
> the simile with files, though. With the coroutine style I could see how the
> most obvious fit would be something like tornado's read_until, or an
> as_lines that essentially calls read_until repeatedly. Can the delimiter for
> this be modified?
>
> My main syntactic gripe is that when I write @inlineCallbacks code or
> monocle code or whatever, when I say "yield" I'm yielding to the reactor.
> That makes sense to me (I realize natural language arguments don't always
> make sense in a programming language context). "yield from" less so (but
> okay, that's what it has to look like). But this just seems weird to me:
>
> yield from trans.send(line.upper())
>
>
> Not only do I not understand why I'm yielding there in the first place (I
> don't have to wait for anything, I just want to push some data out!), it
> feels like all of my yields have been replaced with yield froms for no
> obvious reason (well, there are reasons, I'm just trying to look at this
> naively).
>
> I guess Twisted gets away with this because of deferred chaining: that one
> deferred might have tons of callbacks in the background, many of which also
> doing IO operations, resulting in a sequence of asynchronous operations that
> only at the end cause the generator to be run some more.
>
> I guess that belongs in a different thread, though. Even, then, I'm not sure
> if I'm uncomfortable because I'm seeing something different from what I'm
> used to, or if my argument from English actually makes any sense whatsoever.
>
> Speaking of protocol tests, what would those look like? How do I yell, say,
> "POST /blah HTTP/1.1\r\n" from a transport? Presumably I'd have a mock
> transport, and call the handler with that? (I realize it's early days to be
> thinking that far ahead; I'm just trying to figure out how I can contribute
> a good protocol definition to all of this).
>
> cheers
> lvh
>
>
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