An asyncio example

Ian Kelly ian.g.kelly at
Fri Jul 3 16:38:26 CEST 2015

On Fri, Jul 3, 2015 at 8:31 AM, Ian Kelly <ian.g.kelly at> wrote:
> On Fri, Jul 3, 2015 at 4:28 AM, Adam Bartoš <drekin at> wrote:
>> Hello,
>> I'm experimenting with asyncio. I have composed the following code. There is
>> a server handler and a client handler. I didn't want to split the code into
>> two files so I just used a socketpair, inspired by example
>> . However, my code doesn't work – it blocks because both sides are trying to
>> read more data. But if I close the writer on one side (the commented line),
>> whole connection is closed. So
>> 1) is there a way to close just one direction of the connection?
> No. SOCK_STREAM sockets are always bidirectional.
>> 2) In the blocked situaction even KeyboardInterrupt doesn't break the loop,
>> is that desired behavior? And why?
> I don't think so. When I tried this locally (using Python 3.4.0, so
> replacing "async def" with "def" and "await" with "yield from" and
> "loop.create_task" with "asyncio.async") pressing Ctrl-C did interrupt
> the loop.
>> 3) Are there some other issues with my code with respect to “best practices”
>> how to write a code like this?
> There are a couple of approaches you could take. Since your protocol
> is so far text-based, I would suggest adding '\n' to the ends of your
> messages and using reader.readline instead of
> Alternatively, since the writer isn't planning to write anything
> further after its one message, just call writer.write_eof() (not
> writer.close) after the call to write.

Sorry, the latter approach doesn't work; it's basically equivalent to
calling close. In any case, I suggest using reader.readline.

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