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Python API: how to get the output?

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Balint
Balint on 14 Feb 2017
I would like to call a long-running matlab function from python and print its output while it is running to see the progress. My problem is that out and err is empty if I run with async=True. Why, and how can I fix it? Here is my python code:
import StringIO
import matlab.engine
import time
out = StringIO.StringIO()
err = StringIO.StringIO()
eng = matlab.engine.start_matlab()
future = eng.long_running(5, stdout=out, stderr=err, async=True)
while not future.done():
time.sleep(2)
print 'output', out.getvalue(), err.getvalue()
print 'result', future.result()
eng.quit()
And the matlab function:
function [ result ] = long_running( secs )
%LONG_RUNNING This function runs for a long time and write to stdout
result = 0;
disp('Long_running function started running...')
for i = 1:secs
fprintf('%d iteration\n',i)
result = result + 1;
pause(1);
end
disp('Long_running function finished running.')
end

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Accepted Answer

Bo Li
Bo Li on 14 Feb 2017
When "async" is set to true, the result along with the output/error are not available until "future.result" is called. How about adding "future.result" after the while loop like this?
while not future.done():
time.sleep(2)
future.result()
print 'output', out.getvalue(), err.getvalue()
print 'result', future.result()
eng.quit()

  2 Comments

Balint
Balint on 14 Feb 2017
If there is no way to access the output/error stream while the function is running, than the non-async version can do the job for me. Thanks for the answer!
Sebastián Hernández
Sebastián Hernández on 11 Nov 2017
I need something like this:
...
std_in = StringIO.StringIO()
future = eng.long_running(5, stdout=out, stderr=err, stdin=std_in, async=True)
std_in.write(12)
...
but stdin is not a valid argument. Do you know any way to achieve this? I will run an script that has
a=input('some input')
and I need to pass the input from python.
Thanks!

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