[Tkinter-discuss] python: Display the text on tk window.

[Michael Lange]

Hi,

I forwarded this to the list (hope that's ok), I thought it might be of
interest for other people, too.

On Thu, 18 Jul 2013 13:07:41 +0530
Srinivas Rao <srinivas.rambha at gmail.com> wrote:

> Two pc's are connected with RS 232 label for serial communication. one
> pc for transmitting and other pc for receiving.
> I will run this code in receiving pc.
> This code is to receive text  from a transmitting pc and  display it on
> tkinter window of the receiving  pc.
> The received text has to be displayed on tk window Until it receives
> other text from transmiting pc.
> But With my code the contents of the received text is displaying on tk
> window for only few milliseconds, then after  tk window looks plain
> with no contents of data. When it receives another text from
> transmitter, it again displays the text only for milliseconds and the
> text vanishes.
> 
> Here
> The text is not a pre defined bunch of messages of equal lengh, the
> length of the text vary all the time.
>  The time period between the text's is not constant, it also vary all
> the time.
> The transmitter sends text at differnet time periods,first text in 5
> min, next text may be in 10 min and the third text may be in 30 min and
> so on. I don't want to clear the contents of the text from the tk
> window until it receives next  text from transmitter.
> 
> The font size i choose is 37 and I dont need a scrool bar to scrool the
> window, because transmitter sends maximum of 5 lines to display on
> receiver tk widow.


> import serial
> import threading
> import Queue
> import Tkinter as tk
> 
> 
> class SerialThread(threading.Thread):
>     def __init__(self, queue):
>         threading.Thread.__init__(self)
>         self.queue = queue
>     def run(self):
>         s = serial.Serial('COM11',9600)
>         
>         while True:
>             if s.inWaiting():
>                 text = s.readline(s.inWaiting())
>                 self.queue.put(text)
> 
> class App(tk.Tk):
>     def __init__(self):
>         tk.Tk.__init__(self)
>         self.geometry("1360x750")
>         frameLabel = tk.Frame(self, padx=40, pady =40)
>         self.text = tk.Text(frameLabel, wrap='word',
> font='TimesNewRoman 37', bg=self.cget('bg'), relief='flat')
>         frameLabel.pack()
>         self.text.pack()
>         self.queue = Queue.Queue()
>         thread = SerialThread(self.queue)
>         thread.start()
>         self.process_serial()
> 
>     def process_serial(self):
>         self.text.delete(1.0, 'end')
>         while self.queue.qsize():
>             try:
>                 self.text.insert('end', self.queue.get())
>             except Queue.Empty:
>                 pass
>         self.after(1500, self.process_serial)
> 
> app = App()
> app.mainloop()

Of course the problem here is the call to self.text.delete() in
process_serial() which forces the Text's contents to be deleted after
1500 ms in any case. What you probably intended is something like:

    def process_serial(self):
        while self.queue.qsize():
            try:
                new = self.queue.get()
                self.text.delete(1.0, 'end')
                self.text.insert('end', new)
            except Queue.Empty:
                pass
        self.after(1500, self.process_serial)

which will empty the text only if new content is available (ok, this
does not handle the case of multiple new items in the queue, but I guess
you'll see the point...).

Regards

Michael

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