Python multiprocessing redirect stdout of a child process to a Tkinter Text

Question

I'm trying to use Tkinter GUI to launch a child process and display it stdout/stderr output to a Text widget. Initially, I thought the sys.stdout can be easily redirected to the Text widget by setting "sys.stdout = text_widget" but seems not. It comes to an error: "Text instance has no attribute 'flush'". I checked online and got some solutions, like using a Queue to communicate with the child process. However, none of them fit my case because of my special requirement: - the child process should better be launched by "multiprocessing.Process" because it would be easier to use shared variables, which makes subprocess solutions usable. - the codes of child process are already there with quite a lot "print" inside, so I don't want to modify them to something like "Queue.put()" or else. In this case, could anyone come to a solution of getting a "multiprocessing.Process"'s "print" output and display to a Tkinter Text? Many thanks! An example code of my case is a follows: ``` import sys im…

Accepted Answer

It is still possible to use queues without having to get rid of all of your `print` statements. You can use a `Process` dependent `stdout` redirect to do this. The solution below uses a `Queue` subclass to mimic `stdout`. That queue is then monitored by a thread that looks for new text that gets pumped into the text widget.

```
import sys
import time
from multiprocessing import Process
from multiprocessing.queues import Queue
from threading import Thread
from Tkinter import *

# This function takes the text widget and a queue as inputs.
# It functions by waiting on new data entering the queue, when it 
# finds new data it will insert it into the text widget 
def text_catcher(text_widget,queue):
    while True:
        text_widget.insert(END, queue.get())

# This is a Queue that behaves like stdout
class StdoutQueue(Queue):
    def __init__(self,*args,**kwargs):
        Queue.__init__(self,*args,**kwargs)

def write(self,msg):
        self.put(msg)

def flush(self):
        sys.__stdout__.flush()

def test_child(q):
    # This line only redirects stdout inside the current process 
    sys.stdout = q
    # or sys.stdout = sys.__stdout__ if you want to print the child to the terminal
    print 'child running'

def test_parent(q):
    # Again this only redirects inside the current (main) process
    # commenting this like out will cause only the child to write to the widget 
    sys.stdout = q                                                                                                                                                                                                                                                         
    print 'parent running'
    time.sleep(0.5)
    Process(target=test_child,args=(q,)).start()

if __name__ == '__main__':
    gui_root = Tk()
    gui_txt = Text(gui_root)
    gui_txt.pack()
    q = StdoutQueue()
    gui_btn = Button(gui_root, text='Test', command=lambda:test_parent(q),)
    gui_btn.pack()

# Instantiate and start the text monitor
    monitor = Thread(target=text_catcher,args=(gui_txt,q))
    monitor.daemon = True
    monitor.start()

gui_root.mainloop()
```

Python multiprocessing redirect stdout of a child process to a Tkinter Text

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