Error passing arguments from Java to Python

Question

I'm calling on some Python modules from Java. The module is using numpy, so I'm using Runtime.getRuntime().exec() to call Python. In Java I am doing something like this:

File python = new File("/usr/bin/python2.7");
File script = new File("/opt/my_custom_script.py");
String[] cmdArray = new String[] { python.toString(), script.toString(),
    "-i infile.txt", "-o outfile.txt" };
Process p = Runtime.getRuntime().exec(cmdArray);
p.waitFor();
if (p.exitValue() != 0) {
    throw new Exception(scriptName + " failed with exit code " + p.exitValue());
}

And in Python I've gotten thus far:

def main(argv):
    try:
        opts, args = getopt.getopt(argv, "i:o:")
    except getopt.GetoptError as err:
        print(err)
        sys.exit(128) # made up number so I know when this happens

    sys.exit(0)

if __name__ == "__main__":
    main(sys.argv[1:])

Every time I run this I keep on getting the error number I made up, and my Python script runs no further. Calling on Python directly (in bash) gives me no problems.

Where is my disconnect? How would I go about troubleshooting/debugging this?

Answer 1

Your problem is that you are passing two options two the script rather than the four that getopt expects. That is, -i infile.txt is treated as one option, not, as getopt expects, the two options -i and infile.txt, and the same thing is happening to -o outfile.txt. You can fix this by replacing the line:

String[] cmdArray = new String[] { python.toString(), script.toString(), "-i infile.txt", "-o outfile.txt" };

with this line:

String[] cmdArray = new String[] { python.toString(), script.toString(), "-i", "infile.txt", "-o", "outfile.txt" };

Notice that now -i and infile.txt are now separate array elements, as are -o and -outfile.txt.