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How do I get the Tkinter event-listener to work?

I'm using Tkinter for the GUI of a little tool I wrote with Python. Basically I just want a callback-method to be executed as soon as the contents of an entry widget have changed. This can be done with Tkinter's own variable classes (StringVar, BooleanVar, etc. - see documentation for details: http://effbot.org/tkinterbook/variable.htm).
So I couldn't get the mechanism to work and I found a snippet online, where it works perfectly fine. Now I'm trying to figure out why my version does not work.
As you can see in the two code examples the only difference is, that I'm using the event-listening functionality inside a class, whereas the snippet I found online only demonstrates it in a straight top-to-bottom manner.
Here's what I've already tried:
I instantiated the Tk instance directly in the constructor of my GUI class - same behaviour.
I inherited directly from the Tk class (instead of Frame) - same behaviour.
I placed the callback outside of the class - same behaviour.
The only idea I have is that the problem might be scope related, which I tried to verify.
Working code snippet:
from tkinter import *
import tkinter as tk
def text_changed(*args):
print("Text changed.")
top = tk.Tk()
string_listener = StringVar()
string_listener.set("Init Text")
string_listener.trace("w", text_changed)
entry_widget = tk.Entry(top, textvariable = string_listener)
entry_widget.pack()
top.mainloop()
Not working code snippet
from tkinter import *
import tkinter as tk
root = tk.Tk()
class GUI(tk.Frame):
def __init__(self, master=root):
super(GUI, self).__init__(master)
string_listener = StringVar()
string_listener.set("Init Text")
string_listener.trace("w", self.text_changed_callback)
entry_widget = tk.Entry(master, textvariable=string_listener)
entry_widget.pack()
def text_changed_callback(self, *args):
print("Text changed.")
gui = GUI()
gui.mainloop()
Like in the working example, my code ought to print Text changed., everytime a character is either deleted from or appended to the string in the extry-widget.

The problem is that string_listener is a local variable, and python is destroying the variable when __init__ finishes running. This doesn't happen in your original code since the variable is created in the global scope.
A simple solution is to save a reference as an attribute of the class:
import tkinter as tk
root = tk.Tk()
class GUI(tk.Frame):
def __init__(self, master=root):
super(GUI, self).__init__(master)
self.string_listener = tk.StringVar()
self.string_listener.set("Init Text")
self.string_listener.trace("w", self.text_changed_callback)
entry_widget = tk.Entry(master, textvariable=self.string_listener)
entry_widget.pack()
def text_changed_callback(self, *args):
print("Text changed.")
gui = GUI()
gui.mainloop()
note: I also changed StringVar to tk.StringVar so that I could remove the redundant wildcard import of tkinter.

Audio quiz with Tkinter

I'd like to create a simple quiz with Tkinter (Python 2.7). I have a list of audios and for each of them I want to have the following:
A button that reproduces the audio.
An entry where the user can introduce any text.
A label displaying "Incorrect" by default and "Correct!" whenever the text in the entry is the title of the song in the audio.
I managed to create the three objects, but I'm having a hard time trying to update the label according to the entry text: there are many references around but I couldn't get it working. I guess I do not understand well how the loop works and when events are triggered.
Could you please provide a minimal example that does what I intend to? I provide my code below, but it is very likely to be bloated (I'm totally novice to Tkinter and to object oriented programming) since I basically built it from an existing example in the Internet:
#!/usr/bin/env python
#encoding=utf-8
import Tkinter as tk
import vlc
tk.Tk()
var_entry= tk.StringVar()
var_label= tk.StringVar()
class Application(tk.Frame):
def __init__(self, master=None):
tk.Frame.__init__(self, master)
self.grid()
self.createWidgets()
def createWidgets(self):
self.audio= tk.Button(self,text='Play Audio',command=lambda:vlc.MediaPlayer('./audios/my_audio.mp3').play())
self.audio.grid()
self.entry = tk.Entry(self,width=50,textvariable=var_entry)
self.entry.grid()
var_label.set('Correct!\n' if var_entry.get()=='my_audio_title' else 'Incorrect\n')
self.label = tk.Label(self,textvariable=var_label)
self.label.grid()
self.quitButton = tk.Button(self, text='Quit',command=self.quit)
self.quitButton.grid()
app = Application()
app.master.title('Audio Quiz')
app.mainloop()
I'm sure that the line starting by var_label.set is missplaced, but I don't really know where I should write it and how to make the update for the label.
Thanks in advance.

You can use trace to achieve:
A label displaying "Incorrect" by default and "Correct!" whenever the text in the entry is the title of the song in the audio.
When trace is used with 'w' option, it calls a method whenever the variable class(BooleanVar, DoubleVar, IntVar, StringVar) it is attached to is re-written. Below is an example checking whether the text in the entry is "Valid String" or not:
import tkinter as tk
def check_entry(*args):
global entry, entry_var, label
if entry_var.get() == "Valid String":
label['text'] = "Correct"
else:
label['text'] = "Incorrect"
root = tk.Tk()
entry_var = tk.StringVar()
label = tk.Label(root)
entry = tk.Entry(root, textvariable=entry_var)
label.pack()
entry.pack()
entry_var.trace('w', check_entry)
root.mainloop()

I can't get an image to load on the canvas in Tkinter python

I am having a big issue. The Canvas loads perfectly but the image does not display.
I started Python 1 week ago and I have no clue why does is not working. Can anyone please show me the way to solve the issue of the image not loading on the canvas?
from Tkinter import *
from PIL import ImageTk
from PIL import Image
class Fake_Virus:
def __init__(self, master):
self.master = master
master.title("Totally not a virus!")
b = Button(master, text="Help", command=self.prank)
b.pack(padx=10, pady=10, side=LEFT)
quit = Button(master, text="Close", command=self.close_window)
quit.pack(padx=10, pady=10, side=RIGHT)
photo = PhotoImage("eh.gif")
label = Label(image=photo)
label.image = photo # keep a reference!
label.pack()
f = Frame(master, height=150, width=150)
f.pack_propagate(0) # don't shrink
f.pack()
def prank(self):
print "work"
return
def close_window(self):
root.destroy()
return
root = Tk()
my_gui = Fake_Virus(root)
root.mainloop()

You should use the file option to initialize the photo image object.
This means you need to change photo = PhotoImage("eh.gif") to photo = PhotoImage(file="eh.gif")
Now your code will work. But a working code is not necessarily a good code. There are other issues with your code. Let me go through them quickly:
It is better to code import Tkinter as Tk than from Tkinter import *
Why that hyphen in your class name? Follow PEP8 so that, in the futur, people will find it easy to review and understand your code.
Good that you have written self.master = master (read complete code to know why) but then you have never used it. This means you made a good decision and you render it useless.
You set the title of the window within the initializer. It is better if you do that in a separate function so that whenever you want to add additional settings to your GUI (such as the size, font or whatever) you will only add code to that function instead of vomiting lot of trash inside the initializer which rather needs to be clean.
None of the widgets you created is 'selfed' (you may read Why explicit self has to stay)
It is better you create the widgets in a separate function otherwise your __init__() will be dirty.
Why do you use return in prank() and close_window()? By default, Python functions that do not return something return None anyway so it is useless to code that.
Why did you pack one button to left and the other one to right and then no pack siding for the label? Read about the pack() geometry manager.
Why you did not attach the label to a parent widget as you did for the 2 other buttons? All Tkinter widgets need to be clung into a parent widget. The grand parent of those widgets is an instance of Tkinter.Tk()
Why did you create that frame and then you never used it? You are not doing anything with it, so ..?
Given these remarks, I want to provide you an improved -but not perfect- version of your program. You can then follow this 'philosophy' to add or modifying existing widgets:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import Tkinter as Tk
from PIL import ImageTk
class FakeVirus:
def __init__(self, master):
self.master = master
self.configure_gui()
self.create_widgets()
def configure_gui(self):
self.master.title('Totally not a virus!')
def create_widgets(self):
self.create_buttons()
self.create_label_for_image()
def create_buttons(self):
self.help = Tk.Button(self.master, text='Help', command=self.prank)
self.help.pack(side=Tk.LEFT)
self.quit = Tk.Button(self.master, text='Close', command=self.close_window)
self.quit.pack(side=Tk.LEFT)
def create_label_for_image(self):
self.image_label = Tk.Label(self.master)
self.image_label.pack(side=Tk.LEFT)
self.load_image_to_label()
def load_image_to_label(self):
self.photo = ImageTk.PhotoImage(file='eh.gif')
self.image_label.image = self.photo
self.image_label.config(image=self.photo)
def prank(self):
print "work"
def close_window(self):
root.destroy()
if __name__ == '__main__':
root = Tk.Tk()
my_gui = FakeVirus(root)
root.mainloop()
The output of the above program is:

Python: Tkinter: Multi line scrolling entry box

I would like to make a Tkinter window able to ask for a multi line entry
(so the user will add one or more lines of text)
And then when we clic on the button be able to retrieve the values entered by user for further use.
Until now I have this script:
from Tkinter import *
import ScrolledText
class EntryDemo:
def __init__(self, rootWin):
#Create a entry and button to put in the root window
self.textfield = ScrolledText(rootWin)
#Add some text:
self.textfield.delete(0,END)
self.textfield.insert(0, "Change this text!")
self.textfield.pack()
self.button = Button(rootWin, text="Click Me!", command=self.clicked)
self.button.pack()
def clicked(self):
print("Button was clicked!")
eText = self.textfield.get()
print("The Entry has the following text in it:", eText)
#Create the main root window, instantiate the object, and run the main loop
rootWin = Tk()
#app = EntryDemo( rootWin )
rootWin.mainloop()
But it didn't seem to work, A window appear with nothing inside.
Could you help me?
#########EDIT
New code:
from Tkinter import *
import ScrolledText
class EntryDemo:
def __init__(self, rootWin):
self.textfield = ScrolledText.ScrolledText(rootWin)
#Add some text:
#self.textfield.delete(0,END)
self.textfield.insert(INSERT, "Change this text!")
self.textfield.pack()
self.button = Button(rootWin, text="Click Me!", command=self.clicked)
self.button.pack()
def clicked(self):
eText = self.textfield.get(1.0, END)
print(eText)
rootWin = Tk()
app = EntryDemo( rootWin )
rootWin.mainloop()
Sorry if it look like done with no effort by some down voters (even if I spent more than a day on it) but the Multi line text entry is not exactly what we can call well documented to learn by ourself.

Your first problem is that you commented out the app = EntryDemo( rootWin ) call, so you're not actually doing anything but creating a Tk() root window, then starting its main loop.
If you fix that, your next problem is that you're trying to use the ScrolledText module as if it were a class. You need the ScrolledText.ScrolledText class.
If you fix that, your next problem is that you're trying to delete from an empty text field, which is going to raise some kind of Tcl index error, and then you're also trying to insert at position 0 in an empty text field, which will raise the same error. There's no reason to do the delete at all, and for the insert you probably want to use INSERT as the position.
You still have multiple problems after that, but fixing these three will get your edit box up and displayed so you can start debugging everything else.

A working example based on your code. Note the comment above that both the file you import and the class within the file are named "ScrolledText"
from Tkinter import *
import ScrolledText
class EntryDemo:
def __init__(self, rootWin):
#Create a entry and button to put in the root window
self.textfield = ScrolledText.ScrolledText(rootWin)
self.textfield.pack()
#Add some text:
self.textfield.delete('1.0', END)
self.textfield.insert('insert', "Change this text!")
self.button = Button(rootWin, text="Click Me!",
command=self.clicked)
self.button.pack()
def clicked(self):
print("Button was clicked!")
eText = self.textfield.get('1.0', END)
print("The Entry has the following text in it:", eText)
self.textfield.delete('1.0', END)
rootWin = Tk()
app = EntryDemo( rootWin )
rootWin.mainloop()

TKInter checkbox variable is always 0

I'm using Python's TkInter module for a GUI. Below is a simple checkbox code.
def getCheckVal():
print cbVar.get()
windowTime=Tk.Tk()
cbVar = Tk.IntVar()
btnC = Tk.Checkbutton(windowTime, text="Save", variable = cbVar, command=getCheckVal)
btnC.grid()
windowTime.mainloop()
This code works fine. Each time I tick the checkbox, I get 1, else 0.
However, when I run the same code in a function that is called from another TkInter command (when a button is pressed), it stops working. I always get 0 as the value.
class GUIMainClass:
def __init__(self):
'''Create the main window'''
self.window = Tk.Tk()
def askUser(self):
def getCheckVal():
print cbVar.get()
windowTime=Tk.Tk()
cbVar = Tk.IntVar()
btnC = Tk.Checkbutton(windowTime, text="Save", variable = cbVar,
command=getCheckVal)
btnC.grid()
windowTime.mainloop()
def cmdWindow(self):
frameShow=Tk.Frame(self.window)
frameShow.grid()
btnSwitch = Tk.Button(frameShow, text='Show Plots', command=self.askUser)
btnSwitch.grid()
self.window.mainloop()
GUIObj=GUIMainClass()
GUIObj.cmdWindow()
This is very unusual. What could be going wrong?
EDIT: I've used 2 mainloops because I want a separate window (windowTime) to open up when I click "Show Plots" button. This new window should have the checkbox in it.

Your windowTime, cbVar, etc. variables are defined in the function's local scope. When askUser() completes execution, those values are thrown away. Prepend self. to them to save them as instance variables.
There should only be one mainloop() in your program, to run the main Tkinter root object. Try putting it as the very last line in the program. I recommend doing some reading on Effbot for how to set up a Tkinter application.

I'm not sure what all you're trying to do, but one problem is that the TK.IntVar called cbVar that you create in your askUser() method will be deleted when the function returns, so you need to attach it to something that will still exist after that happens. While you could make it a global variable, a better choice would be to make it an attribute of something more persistent and has a longer "lifespan".
Another likely issue is that generally there should only be one call to mainloop() in a single Tkinter application. It appears what you want to do is display what is commonly known as a Dialog Window, which Tkinter also supports. There's some standard ones built-in, plus some more generic classes to simplify creating custom ones. Here's some documentation I found which describes them in some detail. You may also find it helpful to look at their source code.
In Python 2 it's in the /Lib/lib-tk/tkSimpleDialog.py file and
in Python 3 the code's in a file named /Lib/tkinter/simpledialog.py.
Below is code that takes the latter approach and derives a custom dialog class named GUIButtonDialog from the generic one included the Tkinter library which is simply named Dialog.
try:
import Tkinter as Tk # Python 2
from tkSimpleDialog import Dialog
except ModuleNotFoundError:
import tkinter as Tk # Python 3
from tkinter.simpledialog import Dialog
class GUIButtonDialog(Dialog):
"""Custom one Button dialog box."""
def __init__(self, btnText, parent=None, title=None):
self.btnText = btnText
Dialog.__init__(self, parent, title)
def getCheckVal(self):
print(self.cbVar.get())
def body(self, master):
"""Create dialog body."""
self.cbVar = Tk.IntVar()
self.btnC = Tk.Checkbutton(master, text=self.btnText, variable=self.cbVar,
command=self.getCheckVal)
self.btnC.grid()
return self.btnC # Return the widget to get inital focus.
def buttonbox(self):
# Overridden to suppress default "OK" and "Cancel" buttons.
pass
class GUIMainClass:
def __init__(self):
"""Create the main window."""
self.window = Tk.Tk()
def askUser(self):
"""Display custom dialog window (until user closes it)."""
GUIButtonDialog("Save", parent=self.window)
def cmdWindow(self):
frameShow = Tk.Frame(self.window)
frameShow.grid()
btnSwitch = Tk.Button(frameShow, text='Show Plots', command=self.askUser)
btnSwitch.grid()
self.window.mainloop()
GUIObj = GUIMainClass()
GUIObj.cmdWindow()