passing arguments in python to c executable

Question

I have a c-executable that works as:

./avg filename opt1 opt2 opt3

Eg:

./avg one.dat 1 1 -1

returns something like

 127.504            2.244375804433813           1.111195552742103 blks: 500

When I try to call this from a python code, I have tried:

import os
os.system("./avg one.dat 1 1 -1")

as well as

import subprocess
#args = ("./avg","one.dat","1","1","-1")
args = ("./avg  one.dat  1  1  -1")
popen = subprocess.Popen(args, stdout=subprocess.PIPE)
popen.wait()
output = popen.stdout.read()
print output

Neither works, and the executable that not enough arguments are passed to the executable. It should get at least 4 options.

Any help will be appreciated, thanks in advance.

@PeterWood “the executable [complains] that not enough arguments are passed to the executable” — Konrad Rudolph
– Konrad Rudolph, Commented Mar 7, 2016 at 14:54
Once the application is compiled, the fact it is written in c is meaningless. Removing the tag. — Eugene Sh.
– Eugene Sh., Commented Mar 7, 2016 at 14:55
make your args a tuple ("./avg","one.dat","1","1","-1") . Popen wants the arguments as separate elements in the iterable, not space delineated in a string — en_Knight
– en_Knight, Commented Mar 7, 2016 at 14:56

Antti Haapala · Accepted Answer · 2016-03-07 14:56:47Z

1

You cannot wait() for the subprocess before you read its output; wait waits for the child process to terminate, but child process is blocked writing its output! subprocess.check_output simplifies reading stdout of a process, so you can replace Popen, wait and read with

output = subprocess.check_output(['./avg', 'one.dat', '1', '1', '-1'])

And args = ("./avg","one.dat","1","1","-1") (or a list as above) is the proper way to do it; each argument need to be separate elements in an iterable.

answered Mar 7, 2016 at 14:56

Antti Haapala

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Open AI - Opting Out Over a year ago

You can also use shlex.split to convert './avg one.dat 1 1 -1' to ['./avg', 'one.dat', '1', '1', '-1']

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