Question

I am currently working on a Java project that will allow me to text edit, save, and then execute Python code. I have hit a snag with the execution of this code however.

For executing the code, I have been doing the following:

Process p = Runtime.getRuntime().exec("python someFileName.py",null,new File("someFilePath");

From here, I have a class that takes this process, and tries to take the input and output streams from the process. I have a Timer set with an action listener that will refresh every .01 second.

That is not the problem however. I can receive input just fine if my program consists solely of print statements in python.

If my program contains anything that requires it to block, either raw_input or time.sleep, nothing is displayed.

My actionPerformed method is as follows:

public void actionPerformed(ActionEvent e)
{
    try
    {
        while(inStream.available() > 0)
        {
            System.out.print((char)inStream.read());
        }
        while(errStream.available() > 0)
        {
            System.out.print((char)errStream.read());
        }
    }
    catch(Exception ex)
    {
        ex.printStackTrace();
    }
}

To handle output, I have a KeyListener on a JTextArea that will send the contents of that area to the output stream.

Whenever I have anything in my Python program that requires blocking, no matter what location in the program, the entire thing locks up.

For instance, I have this python program:

import time

print "Welcome to my Program!"
print "Performing calculations"
time.sleep(5)
num = 5
print "Adding 5 to your number"
for x in range(5):
    num+=1
    print num
print "Finished!"

Nothing will display for the time that it sleeps. I would assume that the things I receive in the Java program would be:

Welcome to my Program!
Performing calculations
…then nothing for five seconds…then
Adding 5 to your number
6
7
8
9
10
Finished!

But nothing is displayed at all until after 5 seconds has elapsed. So I can execute the program, wait 5 seconds, then a flood of text appears.

Or for using raw_input, the same thing happens. So in other words I cannot use this to prompt users for input.

I was hoping I could get some help with this blocking issue so that my text displays gradually as opposed to having to wait for everything to get out of the way with timers or input.

Any help or resources are appreciated. My current OS is a Mac, but I want any solution to be workable on Windows as well (if at all possible).

Answer 1

By default, python scripts run with buffered output. That means you may not see any stdout until the script exits and flushes. All you have to do is launch python with -u to request unbuffered output. Then you will see what you were expecting.

python -u someFileName.py