Python API: how to get the output?

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

Answer 1

[Bo Li]

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()

[Balint]

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]

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!