How to call a function on button click.

Here we will learn how to assign an action to button. 

To assign action, command option needs to be used. A value (method / function) assigned to command will be triggered on button click.

below is the code to destroy the main window on click, GUI will look like as above image

 command = action to perform

to call a function,  function  needs to assign to command option. 

IMPORTANT : 

function without parameters can be assigned directly to option command

function with parameters needs to call as lambda so that it get called on click, if a parameterised method / function is assigned without lambda, application will not wait for click on button and directly the function will get called.

 #project to destroy window

 try:
     from Tkinter import *
 except:
     from tkinter import *

 def destroy_win(mw1):
     mw1.destroy()
     mw.destroy()


 def display_message():
     mw1 = Tk()
     mw1.geometry("300x50+130+120")
     mw1.title("AETies")

     lbl = Label(mw1, text="you clicked the hidden message button")
     lbl.pack()

     mw1.mainloop()

 mw = Tk()
 mw.geometry("500x50+50+50")
 mw.title("AETies : Automation Expert Technologies")

 label = Label(mw, text='Please click on button to close window')
 label.pack(side=LEFT)
 btn = Button(mw, text='hidden message', command=display_message)
 btn.pack(side=LEFT)

 mw.mainloop()