Updating a label from an entry field on button push with tkinter in Python 3.5.2

Question

I am trying to create a window with a line label, an entry field, a current value label, and an "Update Value" button.

Here is an example:

This is what I have so far. I can get the entered value to print to console, but I can't seem to work out how to get an entered value and change the currentValue Label to reflect that value by pressing the button:

from tkinter import*
main=Tk()

#StringVar for currentValue in R0C2
currentValue = StringVar(main, "0")

#Called by the setValues button, looks for content in the entry box and updates the "current" label
def setValues():
        content = entry.get()
        print(content)


#This kills the program
def exitProgram():
        exit()

#Title and window size
main.title("Title")
main.geometry("350x200")

#Descriptions on the far left
Label(main, text="Duration (min): ").grid(row=0, column=0)

#Entry boxes for values amidship
entry=Entry(main, width=10)
entry.grid(row=0, column=1)

#Displays what the value is currently set to.
currentValue = Label(textvariable=currentValue)
currentValue.grid(row=0,column=2)

#Takes any inputted values and sets them in the "Current" column using def setValues
setValues=Button(text='Set Values',width=30,command=setValues)
setValues.grid(row=9, column=0, columnspan=2)

#Red button to end program
exitButton=Button(main, text='Exit Program',fg='white',bg='red',width=30, height=1,command=exitProgram)
exitButton.grid(row=20, column = 0, columnspan=2)
main.mainloop()

Answer 1

There are a couple of problems with your code.

Firstly, you are overwriting the setValues function with the setValues Button widget, and similarly, you are overwriting the currentValue StringVar with the currentValue Label.

To set a StringVar, you use its .set method.

Don't use plain exit in a script, that's only meant to be used in an interactive interpreter session, the proper exit function is sys.exit. However, in a Tkinter program you can just call the .destroy method of the root window.

Here's a repaired version of your code.

import tkinter as tk
main = tk.Tk()

#StringVar for currentValue in R0C2
currentValue = tk.StringVar(main, "0")

#Called by the setValues button, looks for content in the entry box and updates the "current" label
def setValues():
    content = entry.get()
    print(content)
    currentValue.set(content)

#This kills the program
def exitProgram():
    main.destroy()

#Title and window size
main.title("Title")
main.geometry("350x200")

#Descriptions on the far left
tk.Label(main, text="Duration (min): ").grid(row=0, column=0)

#Entry boxes for values amidship
entry = tk.Entry(main, width=10)
entry.grid(row=0, column=1)

#Displays what the value is currently set to.
currentValueLabel = tk.Label(textvariable=currentValue)
currentValueLabel.grid(row=0,column=2)

#Takes any inputted values and sets them in the "Current" column using def setValues
setValuesButton = tk.Button(text='Set Values',width=30,command=setValues)
setValuesButton.grid(row=9, column=0, columnspan=2)

#Red button to end program
exitButton = tk.Button(main, text='Exit Program',fg='white',bg='red',width=30, height=1,command=exitProgram)
exitButton.grid(row=20, column = 0, columnspan=2)
main.mainloop()

BTW, it's a Good Idea to avoid "star" imports. Doing from tkinter import * dumps 130 names into your namespace, which is unnecessary and creates the possibility of name collisions, especially if you do star imports from several modules. It also makes the code less readable, since the reader has remember which names you defined and which ones came from the imported module(s).

Answer 2

In my opinion the easiest way to do this would be using an object orientated method. This way you could declare a button with a command that calls a def which runs self.label.configure(text=self.entry.get()).

This can be seen below:

import tkinter as tk

class App:
    def __init__(self, master):
        self.master = master
        self.label = tk.Label(self.master)
        self.entry = tk.Entry(self.master)
        self.button = tk.Button(self.master, text="Ok", command=self.command)
        self.label.pack()
        self.entry.pack()
        self.button.pack()
    def command(self):
        self.label.configure(text=self.entry.get())

root = tk.Tk()
app = App(root)
root.mainloop()

The above creates a label, entry and button. The button has a command which calls a def within the class App and updates the value of the label to be the text contained within the entry.

This all works very smoothly and cleanly and more importantly is drastically easier (in my opinion) to read and update in the future.

Answer 3

From your code you are setting the 'currentValue', which is a StringVar:

#StringVar for currentValue in R0C2
currentValue = StringVar(main, "0")

to an object Label further down in your code. You cannot do this!

 #Displays what the value is currently set to.
    currentValue = Label(textvariable=currentValue) ** this line is wrong
    currentValue.grid(row=0,column=2)

You should name the label something different like:

#Displays what the value is currently set to.
        lblCurrentValue = Label(textvariable=currentValue)
         lblCurrentValue.grid(row=0,column=2)

Then in your "setValues" method you should use 'StringVar.set(value) to update the label like so:

def setValues():
    content = entry.get()
    currentValue.set(entry.get())------------------Here I set the value to the entry box value
    print(content)

I tend to avoid stringVar and just use:

Label.config(text='*label's text*')

If you need more help I can post you my solution but try and solve it first becasue its the best way to learn. My tip is to make sure you are using correct naming conventions. In tkinter I tend to use lbl..., entryBox... etc before widgets so I know what they are and not to confuse them with variables.