Displaying and refreshing my picture every 5 seconds

Question

Ok, I've got the GUI in tkinter working, and I'm trying to grab and image every 5 seconds and display it in a Label named Picturelabel.

from Tkinter import *
from PIL import ImageGrab
import cStringIO, base64, time, threading

class PictureThread(threading.Thread):
    def run(self):
        print "test"
        box = (0,0,500,500) #x,x,width,height
        MyImage = ImageGrab.grab(box)

        fp = cStringIO.StringIO()
        MyImage.save(fp, 'GIF')
        MyPhotoImage = PhotoImage(data=base64.encodestring(fp.getvalue()))

        time.sleep(5)
        PictureThread().run() #If I get rid of this then it just display one image
        return MyPhotoImage

MyVeryNewImage = PictureThread().run()

Picturelabel = Label(BalanceFrame, image=MyVeryNewImage)
Picturelabel.grid(row=3, column=2, columnspan=3)
Picturelabel.image = MyVeryNewImage

window.mainloop()

Firstly how can I clean up this code, as starting a thread inside another thread can't be good practice.

Also when I run this it prints "test" in the console, but it does not bring up the GUI. If I comment out the commented text (PictureThread().run() where I'm creating yet another thread inside it.) then it displays the first image, but not any more.

Answer 1

The problem is that you return the new image from the PictureThread().run() in the method, but you never save it.

How about:

from Tkinter import *
from PIL import ImageGrab
import cStringIO, base64, time, threading

box = (0,0,500,500) #x,x,width,height
MyImage = ImageGrab.grab(box)

fp = cStringIO.StringIO()
MyImage.save(fp, 'GIF')
MyPhotoImage = PhotoImage(data=base64.encodestring(fp.getvalue()))
Picturelabel = Label(BalanceFrame, image=MyPhotoImage)
Picturelabel.grid(row=3, column=2, columnspan=3)

class PictureThread(threading.Thread):
    def run(self):
        while True:
            box = (0,0,500,500) #x,x,width,height
            MyImage = ImageGrab.grab(box)

            fp = cStringIO.StringIO()
            MyImage.save(fp, 'GIF')
            MyPhotoImage = PhotoImage(data=base64.encodestring(fp.getvalue()))

            time.sleep(5)
            Picturelabel.image = MyPhotoImage 

PictureThread().start()

window.mainloop()

Answer 2

You should call start() instead of run(). From the Documentation:

Once a thread object is created, its activity must be started by calling the thread’s start() method. This invokes the run() method in a separate thread of control.

I see you're invoking a new thread inside your run() method. This will cause you to spawn infinite threads!

EDIT: I'm not sure if this works:

from Tkinter import *
from PIL import ImageGrab
import cStringIO, base64, time, threading


Picturelabel = Label(BalanceFrame)
Picturelabel.grid(row=3, column=2, columnspan=3)

class PictureThread(threading.Thread):

    def run(self):
        print "test"
        box = (0,0,500,500) #x,x,width,height
        fp = cStringIO.StringIO()
    while(1):
            MyImage = ImageGrab.grab(box)
            MyImage.save(fp, 'GIF')
            self.image = PhotoImage(data=base64.encodestring(fp.getvalue()))
            Picturelabel.image = self.image
            fp.reset() # reset the fp position to the start
            fp.truncate() # and truncate the file so we don't get garbage 
            time.sleep(5)

PictureThread().start()
window.mainloop()