I'm trying to make a non blocking subprocess call to run a slave.py script from my main.py program. I need to pass args from main.py to slave.py once when it(slave.py) is first started via subprocess.call after this slave.py runs for a period of time then exits.
main.py
for insert, (list) in enumerate(list, start =1):
sys.args = [list]
subprocess.call(["python", "slave.py", sys.args], shell = True)
{loop through program and do more stuff..}
And my slave script
slave.py
print sys.args
while True:
{do stuff with args in loop till finished}
time.sleep(30)
Currently, slave.py blocks main.py from running the rest of its tasks, I simply want slave.py to be independent of main.py, once I've passed args to it. The two scripts no longer need to communicate.
I've found a few posts on the net about non blocking subprocess.call but most of them are centered on requiring communication with slave.py at some-point which I currently do not need. Would anyone know how to implement this in a simple fashion...?
You should use subprocess.Popen
instead of subprocess.call
.
Something like:
subprocess.Popen(["python", "slave.py"] + sys.argv[1:])
From the docs on subprocess.call
:
Run the command described by args. Wait for command to complete, then return the returncode attribute.
(Also don't use a list to pass in the arguments if you're going to use shell = True
).
Here's a MCVE1 example that demonstrates a non-blocking suprocess call:
import subprocess
import time
p = subprocess.Popen(['sleep', '5'])
while p.poll() is None:
print('Still sleeping')
time.sleep(1)
print('Not sleeping any longer. Exited with returncode %d' % p.returncode)
An alternative approach that relies on more recent changes to the python language to allow for co-routine based parallelism is:
# python3.5 required but could be modified to work with python3.4.
import asyncio
async def do_subprocess():
print('Subprocess sleeping')
proc = await asyncio.create_subprocess_exec('sleep', '5')
returncode = await proc.wait()
print('Subprocess done sleeping. Return code = %d' % returncode)
async def sleep_report(number):
for i in range(number + 1):
print('Slept for %d seconds' % i)
await asyncio.sleep(1)
loop = asyncio.get_event_loop()
tasks = [
asyncio.ensure_future(do_subprocess()),
asyncio.ensure_future(sleep_report(5)),
]
loop.run_until_complete(asyncio.gather(*tasks))
loop.close()
1Tested on OS-X using python2.7 & python3.6