Issue using print statement in a thread

[bweiss1258]

I'm having an issue with text output from a thread staying visible in the interpreter. The code below can be used to demonstrate the problem following these steps.

1. Place the code into a file.
2. Start Python 2.7 and import the file.
3. Execute the startThread() function to start the thread.

At this point you should see "hello world" printed every 3 seconds. The issue is that when any key is pressed the all the "hello world" text disappears. I need to find a way to maintain the text printed by the thread in the interpreter. Any ideas or help is appreciated.

from __future__ import print_function
import threading
import time

class TestThread(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self, name='test')
        self._done = False

    def run(self):
        while not self._done:
            print("hello world")
            time.sleep( 3 )

    def close(self):
        self._done = True

td = None
def startThread( ):
    global td
    print( "Starting thread.")
    td = TestThread( )
    td.setDaemon( True )
    td.start( )

[hshivaraj]

You need make sure the main thread stays with the child thread to see the 3 sec frequency. And to do this join the child thread with the main and therefore the main wont exit. Try the following.

td = None
def startThread( ):
    global td
    print( "Starting thread.")
    td = TestThread( )
    td.setDaemon( True )
    td.start( )
    td.join()

[bweiss1258]

Thanks for the response but adding the join prohibits the user from entering commands which needs to be allowed. I just need messages printed by the thread to remain.

[hshivaraj]

def startThread():
    global td
    print("Starting thread.")
    td = TestThread()
    td.setDaemon(True)
    td.start()
    input("Press any key to exit")
    td.close()

[bweiss1258]

Thanks for the response. I don't think this will work either. I don't want to stop the user from entering more python commands. I just need to have both the thread running in the background while the main python interpreter waiting or executing additional commands. I just need the message from the thread to remain visible even if a key is pressed.

[Gribouillis]

The issue is that when any key is pressed the all the "hello world" text disappears.

I don't have this issue in a kubuntu terminal. The bug may be specific to your environment.

[bweiss1258]

I'm running this on Windows because that's what our customer will use but I did try it on a Linux box I have in my office and your right I didn't have an issue. I wonder what's different about python running on Windows that's causing the issue.

[hshivaraj]

How are you running it on windows machine. Command line or do you use IDE?

[snippsat]

I wonder what's different about python running on Windows that's causing the issue.

You should never run thread in IDE/IDLE or editor,always from command line(cmd).
It will/can interfer with the main loop that IDE/IDLE or editor is already running.

If you tell more what you try to solve,we can maybe come up with better a solution.
Example running stuff in schedule Python job scheduling for humans.

[bweiss1258]

I'm running from the command line. For the project I'm on the thread is polling a target to determine if an event has occurred and if so outputs a message to the console indicating that an event was detected. The user can then enter commands at the python prompt for more info. I've tried the example code I post on Linux and on my Mac and don't not have the issues I'm seeing on my Windows PC.