Python Tkinter Text Widget with Auto & Custom Scroll

Question

I wrote a simple Tkinter based Python application that reads text from a serial connection and adds it to the window, specifically a text widged.

After a lot of tweaks a

Answer 1

OK,

based on the valuable suggestions by noob oddy I was able to rewrite the example script by using the Tkinter.generate_event() method to generate asynchronous event and a queue to pass the information.

Every time a line is read from the stream (which is simulated by a constant string and a delay), I append the line to a queue (because passing objects to the event method is not supported AFAIK) and then create a new event.

The event callback method retrieves the message from the queue and adds it to the Text widged. This works because this method is called from the Tkinter mainloop an thus it cannot interfere with the other jobs.

Here is the script:

import re,sys,time
from Tkinter import *
import Tkinter
import threading
import traceback
import Queue


class ReaderThread(threading.Thread): 
    def __init__(self, root, queue):
        print "Thread init"
        threading.Thread.__init__(self) 
        self.root = root
        self.running = True
        self.q = queue

    def stop(self):
        print "Stopping thread"
        running = False

    def run(self):
        print "Thread started"
        time.sleep(5)

        try:
            while(self.running):
                # emulating delay when reading from serial interface
                time.sleep(0.05)
                curline = "the quick brown fox jumps over the lazy dog\n"

                try:
                    self.q.put(curline)
                    self.root.event_generate('<<AppendLine>>', when='tail')
                # If it failed, the window has been destoyed: over
                except TclError as e:
                    print e
                    break

        except Exception as e:
            traceback.print_exc(file=sys.stdout)
            print "Exception in receiver thread, stopping..."
            pass
        print "Thread stopped"


class Transformer:
    def __init__(self):
        self.q = Queue.Queue()
        self.lineIndex = 1
        pass

    def appendLine(self, event):
        line = self.q.get_nowait()

        if line == None:
            return

        i = self.lineIndex
        curIndex = "1.0"
        lowerEdge = 1.0
        pos = 1.0

        # get cur position
        pos = self.scrollbar.get()[1]

        # Disable scrollbar
        self.text.configure(yscrollcommand=None, state=NORMAL)

        # Add to text window
        self.text.insert(END, str(line))
        startIndex = repr(i) + ".0"
        curIndex = repr(i) + ".end"

        # Perform colorization
        if i % 6 == 0:
            self.text.tag_add("warn", startIndex, curIndex)
        elif i % 6 == 1:
            self.text.tag_add("debug", startIndex, curIndex)                            
        elif i % 6 == 2:
            self.text.tag_add("info", startIndex, curIndex)                         
        elif i % 6 == 3:
            self.text.tag_add("error", startIndex, curIndex)                            
        elif i % 6 == 4:
            self.text.tag_add("fatal", startIndex, curIndex)                            
        i = i + 1

        # Enable scrollbar
        self.text.configure(yscrollcommand=self.scrollbar.set, state=DISABLED)

        # Auto scroll down to the end if scroll bar was at the bottom before
        # Otherwise allow customer scrolling                        

        if pos == 1.0:
            self.text.yview(END)

        self.lineIndex = i

    def start(self):
        """starts to read linewise from self.in_stream and parses the read lines"""
        count = 1
        self.root = Tk()
        self.root.title("Tkinter Auto-Scrolling Test")#
        self.root.bind('<<AppendLine>>', self.appendLine)
        self.topPane = PanedWindow(self.root, orient=HORIZONTAL)
        self.topPane.pack(side=TOP, fill=X)
        self.lowerPane = PanedWindow(self.root, orient=VERTICAL)

        self.scrollbar = Scrollbar(self.root)
        self.scrollbar.pack(side=RIGHT, fill=Y)
        self.text = Text(wrap=WORD, yscrollcommand=self.scrollbar.set)
        self.scrollbar.config(command=self.text.yview)
        # Color definition for log levels
        self.text.tag_config("debug",foreground="gray50")
        self.text.tag_config("info",foreground="green")
        self.text.tag_config("warn",foreground="orange")
        self.text.tag_config("error",foreground="red")
        self.text.tag_config("fatal",foreground="#8B008B")
        # set default color
        self.text.config(background="black", foreground="gray");
        self.text.pack(expand=YES, fill=BOTH)       

        self.lowerPane.add(self.text)
        self.lowerPane.pack(expand=YES, fill=BOTH)

        t = ReaderThread(self.root, self.q)
        print "Starting thread"
        t.start()

        try:
            self.root.mainloop()
        except Exception as e:
            print "Exception in window manager: ", e

        t.stop()
        t.join()


if __name__ == "__main__":
    try:
        trans = Transformer()
        trans.start()
    except Exception as e:
        print "Error: ", e
        sys.exit(1)     

Thanks again to everybody who contributed for your help!

Answer 2

It's hard to tell what's really going on but have you considered using a Queue?

from Tkinter import *
import time, Queue, thread

def simulate_input(queue):
    for i in range(100):
        info = time.time()
        queue.put(info)
        time.sleep(0.5)

class Demo:
    def __init__(self, root, dataQueue):
        self.root = root
        self.dataQueue = dataQueue

        self.text = Text(self.root, height=10)
        self.scroller = Scrollbar(self.root, command=self.text.yview)
        self.text.config(yscrollcommand=self.scroller.set)
        self.text.tag_config('newline', background='green')
        self.scroller.pack(side='right', fill='y')
        self.text.pack(fill='both', expand=1)

        self.root.after_idle(self.poll)

    def poll(self):
        try:
            data = self.dataQueue.get_nowait()
        except Queue.Empty:
            pass
        else:
            self.text.tag_remove('newline', '1.0', 'end')
            position = self.scroller.get()
            self.text.insert('end', '%s\n' %(data), 'newline')            
            if (position[1] == 1.0):
                self.text.see('end')
        self.root.after(1000, self.poll)

q = Queue.Queue()
root = Tk()
app = Demo(root, q)

worker = thread.start_new_thread(simulate_input, (q,))
root.mainloop()

Answer 3

Regarding your demo script.

You're doing GUI stuff from the non-GUI thread. That tends to cause problems.

see: http://www.effbot.org/zone/tkinter-threads.htm