[Python-Dev] Status of PEP 3145 (original) (raw)

[Python-Dev] Status of PEP 3145 - Asynchronous I/O for subprocess.popen

Terry Reedy tjreedy at udel.edu
Fri Mar 28 21:58:25 CET 2014

On 3/28/2014 6:20 AM, Victor Stinner wrote:

Full example of asynchronous communication with a subprocess (the python interactive interpreter) using asyncio high-level API:

Thank you for writing this. As I explained in response to Josiah, Idle communicates with a python interpreter subprocess through a socket. Since making the connection is not dependable, I would like to replace the socket with the pipes. http://bugs.python.org/issue18823

However, the code below creates a subprocess for one command and one response, which can apparently be done now with subprocess.communicate. What I and others need is a continuing (non-blocking) conversion with 1 and only 1 subprocess (see my response to Josiah), and that is much more difficult. So this code does not do what he claims his will do.

However it is done, I agree with the intent of the PEP to make it much easier to talk with a subprocess. Victor, if you can rewrite the below with a run_forever loop that can accept new write-read task pairs and also make each line read immediately accessible, that would be really helpful. Post it on the issue above if you prefer.

Another difference from what you wrote below and what Idle does today is that the shell, defined in idlelib/PyShell.py, does not talk to the subprocess interpreter directly but to a run supervisor defined in idlelib/run.py through an rpc protocol ('cmd', 'arg string'). To use the pipes, the supervisor would grab all input from stdin (instead of the socket) and exec user code as it does today, or it could be replaced by a supervisor class with an instance with a name like idle_supervisor_3_4_0 that would be extremely unlikely to clash with any name created by users.

--- import asyncio.subprocess import time import sys

@asyncio.coroutine def evalpythonasync(command, encoding='ascii', loop=None): proc = yield from asyncio.subprocess.createsubprocessexec( sys.executable, "-u", "-i", stdin=asyncio.subprocess.PIPE, stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.STDOUT, loop=loop) # wait for the prompt buffer = bytearray() while True: data = yield from proc.stdout.read(100) buffer.extend(data) if buffer.endswith(b'>>> '): break proc.stdin.write(command.encode(encoding) + b"\n") yield from proc.stdin.drain() proc.stdin.close() output = yield from proc.stdout.read() output = output.decode(encoding) output = output.rstrip() if output.endswith('>>>'): output = output[:-3].rstrip() return output def evalpython(command, timeout=None): loop = asyncio.geteventloop() task = asyncio.Task(evalpythonasync(command, loop=loop), loop=loop) return loop.rununtilcomplete(asyncio.waitfor(task, timeout)) def testsequential(nproc, command): t0 = time.monotonic() for index in range(nproc): evalpython(command) return time.monotonic() - t0 def testparallel(nproc, command): loop = asyncio.geteventloop() tasks = [asyncio.Task(evalpythonasync(command, loop=loop), loop=loop) for index in range(nproc)] t0 = time.monotonic() loop.rununtilcomplete(asyncio.wait(tasks)) return time.monotonic() - t0 print("1+1 = %r" % evalpython("1+1", timeout=1.0)) slowcode = "import math; print(str(math.factorial(20000)).count('7'))" dt = testsequential(10, slowcode) print("Run 10 tasks in sequence: %.1f sec" % dt) dt2 = testparallel(10, slowcode) print("Run 10 tasks in parallel: %.1f sec (speed=%.1f)" % (dt2, dt/dt2)) # cleanup asyncio asyncio.geteventloop().close()

-- Terry Jan Reedy

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