How to update matplotlib with Scale widget in Tkinter

you need to use the command= argument to Scale to call a function every time the widget is modified. In this function, you can update your plot.

The code is a little messy because you have to have access to your numpy array and the axes and canvas in that function, but this works:

import numpy as np
from Tkinter import *
from ttk import *
import matplotlib
matplotlib.use('TkAgg')
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg, NavigationToolbar2TkAgg
from matplotlib.backend_bases import key_press_handler
from matplotlib.figure import Figure




def on_key_event(event):
   print('you pressed %s'%event.key)
   key_press_handler(event, canvas, toolbar)

def mOpen():
   global t
   global a
   global canvas_3

   var = IntVar()
   slider_1 = Scale(mGui,orient=HORIZONTAL,length = 100,from_=0,to=9, variable=var, command=updateScale)
   slider_1.place(x = 765,y=390)
   t = np.random.random_sample(100000).reshape(100,100,10)
   f = Figure(figsize=(5,4),dpi=100)
   a = f.add_subplot(111)
   a.imshow(t[:,:,var.get()])
   print var.get()
   canvas_3 = FigureCanvasTkAgg(f,master = mGui)
   canvas_3.show()
   canvas_3.get_tk_widget().place(x=5,y=5)
   toolbar_3 = NavigationToolbar2TkAgg( canvas_3, mGui )
   toolbar_3.update()
   toolbar_3.place(x=10,y=15)
   canvas_3._tkcanvas.place(x=7,y=7)
   canvas_3.mpl_connect('key_press_event', on_key_event)

def updateScale(var):
   print "scale is now %s" % (var)
   a.imshow(t[:,:,int(float(var))])
   canvas_3.show()

mGui = Tk()                     
mOpen()
mGui.geometry('900x900+300+10') 
mGui.title('Plot')
mGui.mainloop()