How can I call an external program with a python script and retrieve the output and return code?
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2There are some existing questions and answers on SO that will help you: stackoverflow.com/questions/89228/…Jarret Hardie– Jarret Hardie2009-04-01 19:27:37 +00:00Commented Apr 1, 2009 at 19:27
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Does this answer your question? How to execute a program or call a system command?robertspierre– robertspierre2021-11-20 10:33:29 +00:00Commented Nov 20, 2021 at 10:33
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Can anyone tell me how to store the output to a log.csv file (I need this for git, so the csv file is git commit history)vpp– vpp2022-03-17 16:50:49 +00:00Commented Mar 17, 2022 at 16:50
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6 Answers
Look at the subprocess module: a simple example follows...
from subprocess import Popen, PIPE
process = Popen(["ls", "-la", "."], stdout=PIPE)
(output, err) = process.communicate()
exit_code = process.wait()
5 Comments
Ben McCann
I've edited the answer above to reflect Ambroz's suggestion in case someone does not read the comments and uses the previously incorrect code.
ntg
if this does not for some reason work, you might want to add shell=True to the params ( when in windows? )
patryk.beza
It seems that the above solution can be replaced by simple call
subprocess.run() (Python >= 3.5 is required).
Kumar Saptam
can I get the line number of error line like a line has error and the function returns me the line number like 1.0? so that I can add a tag and highlight the error.
HmT
In order to grab the error outputs "stderr=PIPE" should also be added:
process = Popen(["ls", "-la", "."], stdout=PIPE, stderr=PIPE)Following Ambroz Bizjak's previous comment, here is a solution that worked for me:
import shlex
from subprocess import Popen, PIPE
cmd = "..."
process = Popen(shlex.split(cmd), stdout=PIPE)
process.communicate()
exit_code = process.wait()
2 Comments
dotancohen
This is by far the best answer.
After some research, I have the following code which works very well for me. It basically prints both stdout and stderr in real time. Hope it helps someone else who needs it.
stdout_result = 1
stderr_result = 1
def stdout_thread(pipe):
global stdout_result
while True:
out = pipe.stdout.read(1)
stdout_result = pipe.poll()
if out == '' and stdout_result is not None:
break
if out != '':
sys.stdout.write(out)
sys.stdout.flush()
def stderr_thread(pipe):
global stderr_result
while True:
err = pipe.stderr.read(1)
stderr_result = pipe.poll()
if err == '' and stderr_result is not None:
break
if err != '':
sys.stdout.write(err)
sys.stdout.flush()
def exec_command(command, cwd=None):
if cwd is not None:
print '[' + ' '.join(command) + '] in ' + cwd
else:
print '[' + ' '.join(command) + ']'
p = subprocess.Popen(
command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, cwd=cwd
)
out_thread = threading.Thread(name='stdout_thread', target=stdout_thread, args=(p,))
err_thread = threading.Thread(name='stderr_thread', target=stderr_thread, args=(p,))
err_thread.start()
out_thread.start()
out_thread.join()
err_thread.join()
return stdout_result + stderr_result
1 Comment
ashrasmun
I only copy pasted the code to see if it works and I got an error that
out is of type bytes so it cannot be used in the write method. Also, it prints the characters, but never stops.Check out the subprocess module here: http://docs.python.org/library/subprocess.html#module-subprocess. It should get what you need done.
Comments
I've developed a little library (py-execute) that allows you to execute external programs, retrieve the output and the retcode and, at the same time get output in console in real time:
>>> from py_execute.process_executor import execute
>>> ret = execute('echo "Hello"')
Hello
>>> ret
(0, 'Hello\n')
You can avoid printing to console passing a mock user_io:
>>> from mock import Mock
>>> execute('echo "Hello"', ui=Mock())
(0, 'Hello\n')
I wrote it because with plain Popen (In Python 2.7) I was having trouble executing commands with a long output
Comments
I know this is a pretty old thread, but I wanted to add something I found while researching this since I stumbled on this and it helped me quite a bit.
In subprocess, if you don't need total control over PIPE you can use
the .run() function.
This is my current code that works rather nicely for my own program.
process = subprocess.run(["./program","cm1","cm2"], text=True)
print(process)
And this outputs the stdout live. This can also be configured to output both stdout and stderr in the same stream.
