[Tutor] Finding error from os.system(cmd)

[Steven D'Aprano]

Kann Vearasilp wrote:
> Dear all,
> 
> I tried using python to execute some external java program in my code.
> My problem is the os.system(cmd) was not working properly while

Define "not working properly".


My guess is that you're probably getting an exception

OSError: [Errno 2] No such file or directory

before os.system is even called. For the code you give to even have a 
hope of working correctly, you need to call it from the current 
directory containing:

current directory:
     tmp/medusa
     mirnaworkbench/Medusa/Medusa.jar

otherwise abspath will fail and os.system will not even be called.



> executing 'java' from terminal worked just fine. I am not sure what is
> wrong here. 

In the Python code you give, you don't just execute "java", you execute 
a fairly complex command line. What happens when you execute that 
*exact* same line from the terminal, not just "java"?




> Is there a way to print out/detect error in my code for
> this case?

os.system(cmd) will print any output to the terminal, just as if you ran 
it from the terminal yourself. Open a Python interactive interpreter, 
and run os.system(cmd) at the prompt, and read the output.


-- 
Steven