How do you run your own code alongside Tkinter s event loop

Question

My little brother is just getting into programming  and for his Science Fair project  he s doing a simulation of a flock of birds in the sky  He s gotten most of his code written  and it works nicely  but the birds need to move every moment   Tkinter  however  hogs the time for its own event loop  and so his code won t run  Doing root mainloop   runs  runs  and keeps running  and the only thing it runs is the event handlers   Is there a way to have his code run alongside the mainloop  without multithreading  it s confusing and this should be kept simple   and if so  what is it   Right now  he came up with an ugly hack  tying his move   function to  lt b1-motion gt   so that as long as he holds the button down and wiggles the mouse  it works  But there s got to be a better way

User · Answer

The solution posted by Bjorn results in a "RuntimeError: Calling Tcl from different appartment" message on my computer (RedHat Enterprise 5, python 2.6.1). Bjorn might not have gotten this message, since, according to one place I checked, mishandling threading with Tkinter is unpredictable and platform-dependent.

The problem seems to be that app.start() counts as a reference to Tk, since app contains Tk elements. I fixed this by replacing app.start() with a self.start() inside __init__. I also made it so that all Tk references are either inside the function that calls mainloop() or are inside functions that are called by the function that calls mainloop() (this is apparently critical to avoid the "different apartment" error).

Finally, I added a protocol handler with a callback, since without this the program exits with an error when the Tk window is closed by the user.

The revised code is as follows:

# Run tkinter code in another thread

import tkinter as tk
import threading

class App(threading.Thread):

    def __init__(self):
        threading.Thread.__init__(self)
        self.start()

    def callback(self):
        self.root.quit()

    def run(self):
        self.root = tk.Tk()
        self.root.protocol("WM_DELETE_WINDOW", self.callback)

        label = tk.Label(self.root, text="Hello World")
        label.pack()

        self.root.mainloop()


app = App()
print('Now we can continue running code while mainloop runs!')

for i in range(100000):
    print(i)

User · Answer

Use the after method on the Tk object   from tkinter import    root   Tk    def task        print  hello       root after 2000  task     reschedule event in 2 seconds  root after 2000  task  root mainloop     Here s the declaration and documentation for the after method   def after self  ms  func None   args          Call function once after given time       MS specifies the time in milliseconds  FUNC gives the     function which shall be called  Additional parameters     are given as parameters to the function call   Return     identifier to cancel scheduling with after cancel

User · Answer

Another option is to let tkinter execute on a separate thread  One way of doing it is like this   import Tkinter import threading  class MyTkApp threading Thread       def   init   self           self root Tkinter Tk           self s   Tkinter StringVar           self s set  Foo           l   Tkinter Label self root textvariable self s          l pack           threading Thread   init   self       def run self           self root mainloop     app   MyTkApp   app start      Now the app should be running and the value shown on the label   can be changed by changing the member variable s    Like this    app s set  Bar     Be careful though  multithreaded programming is hard and it is really easy to shoot your self in the foot  For example you have to be careful when you change member variables of the sample class above so you don t interrupt with the event loop of Tkinter

User · Answer

When writing your own loop  as in the simulation  I assume   you need to call the update function which does what the mainloop does  updates the window with your changes  but you do it in your loop   def task         do something    root update    while 1     task

User · Answer

The solution posted by Bjorn results in a "RuntimeError: Calling Tcl from different appartment" message on my computer (RedHat Enterprise 5, python 2.6.1). Bjorn might not have gotten this message, since, according to one place I checked, mishandling threading with Tkinter is unpredictable and platform-dependent.

The problem seems to be that app.start() counts as a reference to Tk, since app contains Tk elements. I fixed this by replacing app.start() with a self.start() inside __init__. I also made it so that all Tk references are either inside the function that calls mainloop() or are inside functions that are called by the function that calls mainloop() (this is apparently critical to avoid the "different apartment" error).

Finally, I added a protocol handler with a callback, since without this the program exits with an error when the Tk window is closed by the user.

The revised code is as follows:

# Run tkinter code in another thread

import tkinter as tk
import threading

class App(threading.Thread):

    def __init__(self):
        threading.Thread.__init__(self)
        self.start()

    def callback(self):
        self.root.quit()

    def run(self):
        self.root = tk.Tk()
        self.root.protocol("WM_DELETE_WINDOW", self.callback)

        label = tk.Label(self.root, text="Hello World")
        label.pack()

        self.root.mainloop()


app = App()
print('Now we can continue running code while mainloop runs!')

for i in range(100000):
    print(i)

User · Answer

This is the first working version of what will be a GPS reader and data presenter   tkinter is a very fragile thing with way too few error messages   It does not put stuff up and does not tell why much of the time   Very difficult coming from a good WYSIWYG form developer   Anyway  this runs a small routine 10 times a second and presents the information on a form   Took a while to make it happen   When I tried a timer value of 0  the form never came up   My head now hurts   10 or more times per second is good enough for me   I hope it helps someone else   Mike Morrow  import tkinter as tk import time  def GetDateTime        Get current date and time in ISO8601     https   en wikipedia org wiki ISO 8601      https   xkcd com 1179    return  time strftime   Y m d   time gmtime               time strftime   H M S   time gmtime               time strftime   Y m d   time localtime               time strftime   H M S   time localtime      class Application tk Frame      def   init   self  master        fontsize   12     textwidth   9      tk Frame   init   self  master      self pack        tk Label self  font   Helvetica   fontsize   bg     be004e   fg    white   width   textwidth               text  Local Time   grid row 0  column 0      self LocalDate   tk StringVar       self LocalDate set  waiting          tk Label self  font   Helvetica   fontsize   bg     be004e   fg    white   width   textwidth               textvariable self LocalDate  grid row 0  column 1       tk Label self  font   Helvetica   fontsize   bg     be004e   fg    white   width   textwidth               text  Local Date   grid row 1  column 0      self LocalTime   tk StringVar       self LocalTime set  waiting          tk Label self  font   Helvetica   fontsize   bg     be004e   fg    white   width   textwidth               textvariable self LocalTime  grid row 1  column 1       tk Label self  font   Helvetica   fontsize   bg     40CCC0   fg    white   width   textwidth               text  GMT Time   grid row 2  column 0      self nowGdate   tk StringVar       self nowGdate set  waiting          tk Label self  font   Helvetica   fontsize   bg     40CCC0   fg    white   width   textwidth               textvariable self nowGdate  grid row 2  column 1       tk Label self  font   Helvetica   fontsize   bg     40CCC0   fg    white   width   textwidth               text  GMT Date   grid row 3  column 0      self nowGtime   tk StringVar       self nowGtime set  waiting          tk Label self  font   Helvetica   fontsize   bg     40CCC0   fg    white   width   textwidth               textvariable self nowGtime  grid row 3  column 1       tk Button self  text  Exit   width   10  bg     FF8080   command root destroy  grid row 4  columnspan 2       self gettime     pass    def gettime self       gdt  gtm  ldt  ltm   GetDateTime       gdt   gdt 0 4          gdt 4 6          gdt 6 8      gtm   gtm 0 2          gtm 2 4          gtm 4 6      Z        ldt   ldt 0 4          ldt 4 6          ldt 6 8      ltm   ltm 0 2          ltm 2 4          ltm 4 6        self nowGtime set gdt      self nowGdate set gtm      self LocalTime set ldt      self LocalDate set ltm       self after 100  self gettime      print  ltm     Prove it is running this and the external code  too    pass  root   tk Tk   root wm title  Temp Converter   app   Application master root   w   200   width for the Tk root h   125   height for the Tk root    get display screen width and height ws   root winfo screenwidth      width of the screen hs   root winfo screenheight     height of the screen    calculate x and y coordinates for positioning the Tk root window   centered  x    ws 2  -  w 2   y    hs 2  -  h 2    right bottom corner  misfires in Win10 putting it too low  OK in Ubuntu  x   ws - w y   hs - h - 35    -35 fixes it  more or less  for Win10   set the dimensions of the screen and where it is placed root geometry   dx d  d  d     w  h  x  y    root mainloop

User · Answer

Use the after method on the Tk object   from tkinter import    root   Tk    def task        print  hello       root after 2000  task     reschedule event in 2 seconds  root after 2000  task  root mainloop     Here s the declaration and documentation for the after method   def after self  ms  func None   args          Call function once after given time       MS specifies the time in milliseconds  FUNC gives the     function which shall be called  Additional parameters     are given as parameters to the function call   Return     identifier to cancel scheduling with after cancel

User · Answer

This is the first working version of what will be a GPS reader and data presenter   tkinter is a very fragile thing with way too few error messages   It does not put stuff up and does not tell why much of the time   Very difficult coming from a good WYSIWYG form developer   Anyway  this runs a small routine 10 times a second and presents the information on a form   Took a while to make it happen   When I tried a timer value of 0  the form never came up   My head now hurts   10 or more times per second is good enough for me   I hope it helps someone else   Mike Morrow  import tkinter as tk import time  def GetDateTime        Get current date and time in ISO8601     https   en wikipedia org wiki ISO 8601      https   xkcd com 1179    return  time strftime   Y m d   time gmtime               time strftime   H M S   time gmtime               time strftime   Y m d   time localtime               time strftime   H M S   time localtime      class Application tk Frame      def   init   self  master        fontsize   12     textwidth   9      tk Frame   init   self  master      self pack        tk Label self  font   Helvetica   fontsize   bg     be004e   fg    white   width   textwidth               text  Local Time   grid row 0  column 0      self LocalDate   tk StringVar       self LocalDate set  waiting          tk Label self  font   Helvetica   fontsize   bg     be004e   fg    white   width   textwidth               textvariable self LocalDate  grid row 0  column 1       tk Label self  font   Helvetica   fontsize   bg     be004e   fg    white   width   textwidth               text  Local Date   grid row 1  column 0      self LocalTime   tk StringVar       self LocalTime set  waiting          tk Label self  font   Helvetica   fontsize   bg     be004e   fg    white   width   textwidth               textvariable self LocalTime  grid row 1  column 1       tk Label self  font   Helvetica   fontsize   bg     40CCC0   fg    white   width   textwidth               text  GMT Time   grid row 2  column 0      self nowGdate   tk StringVar       self nowGdate set  waiting          tk Label self  font   Helvetica   fontsize   bg     40CCC0   fg    white   width   textwidth               textvariable self nowGdate  grid row 2  column 1       tk Label self  font   Helvetica   fontsize   bg     40CCC0   fg    white   width   textwidth               text  GMT Date   grid row 3  column 0      self nowGtime   tk StringVar       self nowGtime set  waiting          tk Label self  font   Helvetica   fontsize   bg     40CCC0   fg    white   width   textwidth               textvariable self nowGtime  grid row 3  column 1       tk Button self  text  Exit   width   10  bg     FF8080   command root destroy  grid row 4  columnspan 2       self gettime     pass    def gettime self       gdt  gtm  ldt  ltm   GetDateTime       gdt   gdt 0 4          gdt 4 6          gdt 6 8      gtm   gtm 0 2          gtm 2 4          gtm 4 6      Z        ldt   ldt 0 4          ldt 4 6          ldt 6 8      ltm   ltm 0 2          ltm 2 4          ltm 4 6        self nowGtime set gdt      self nowGdate set gtm      self LocalTime set ldt      self LocalDate set ltm       self after 100  self gettime      print  ltm     Prove it is running this and the external code  too    pass  root   tk Tk   root wm title  Temp Converter   app   Application master root   w   200   width for the Tk root h   125   height for the Tk root    get display screen width and height ws   root winfo screenwidth      width of the screen hs   root winfo screenheight     height of the screen    calculate x and y coordinates for positioning the Tk root window   centered  x    ws 2  -  w 2   y    hs 2  -  h 2    right bottom corner  misfires in Win10 putting it too low  OK in Ubuntu  x   ws - w y   hs - h - 35    -35 fixes it  more or less  for Win10   set the dimensions of the screen and where it is placed root geometry   dx d  d  d     w  h  x  y    root mainloop

User · Answer

Use the after method on the Tk object   from tkinter import    root   Tk    def task        print  hello       root after 2000  task     reschedule event in 2 seconds  root after 2000  task  root mainloop     Here s the declaration and documentation for the after method   def after self  ms  func None   args          Call function once after given time       MS specifies the time in milliseconds  FUNC gives the     function which shall be called  Additional parameters     are given as parameters to the function call   Return     identifier to cancel scheduling with after cancel

User · Answer

Another option is to let tkinter execute on a separate thread  One way of doing it is like this   import Tkinter import threading  class MyTkApp threading Thread       def   init   self           self root Tkinter Tk           self s   Tkinter StringVar           self s set  Foo           l   Tkinter Label self root textvariable self s          l pack           threading Thread   init   self       def run self           self root mainloop     app   MyTkApp   app start      Now the app should be running and the value shown on the label   can be changed by changing the member variable s    Like this    app s set  Bar     Be careful though  multithreaded programming is hard and it is really easy to shoot your self in the foot  For example you have to be careful when you change member variables of the sample class above so you don t interrupt with the event loop of Tkinter

User · Answer

When writing your own loop  as in the simulation  I assume   you need to call the update function which does what the mainloop does  updates the window with your changes  but you do it in your loop   def task         do something    root update    while 1     task

User · Answer

Use the after method on the Tk object   from tkinter import    root   Tk    def task        print  hello       root after 2000  task     reschedule event in 2 seconds  root after 2000  task  root mainloop     Here s the declaration and documentation for the after method   def after self  ms  func None   args          Call function once after given time       MS specifies the time in milliseconds  FUNC gives the     function which shall be called  Additional parameters     are given as parameters to the function call   Return     identifier to cancel scheduling with after cancel

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