

Almost every application needs to communicate with the user in some way.
Therefore, a substantial part of the code deals with the interaction
of program logic with GUI components.

Typically, the following is needed:

 put values into input fields under program control
 read and check input from the user
 pop up dialogs to query the user for further information


Task

For a minimal "application", write a program that presents a form with three components to the user:

 a numeric input field ("Value") 
 a button ("increment")
 a button ("random")


The field is initialized to zero.

The user may manually enter a new value into the field,
or increment its value with the "increment" button.

Entering a non-numeric value should be either impossible,
or issue an error message.

Pressing the "random" button presents a confirmation dialog,
and resets the field's value to a random value if the answer is "Yes".

(This task may be regarded as an extension of the task Simple windowed application).



 
import random, tkMessageBox
from Tkinter import *
window = Tk()
window.geometry("300x50+100+100")
options = { "padx":5, "pady":5}
s=StringVar()
s.set(1)
def increase():
    s.set(int(s.get())+1)
def rand():
    if tkMessageBox.askyesno("Confirmation", "Reset to random value ?"):
        s.set(random.randrange(0,5000))
def update(e):
    if not e.char.isdigit():
        tkMessageBox.showerror('Error', 'Invalid input !') 
        return "break"
e = Entry(text=s)
e.grid(column=0, row=0, **options)
e.bind('<Key>', update)
b1 = Button(text="Increase", command=increase, **options )
b1.grid(column=1, row=0, **options)
b2 = Button(text="Random", command=rand, **options)
b2.grid(column=2, row=0, **options)
mainloop()