Cambridge IGCSE and O Level Programming Book
# hello-gui.py # Import everything required from the tkinter module from tkinter import * # Function called by clicking my_button: def change_text(): my_label.config(text='Hello World') # Create the main tkinter window window = Tk() window.title('My Application') # Add an empty tkinter label widget and place it in a grid layout my_label = Label(window, width=25, height=1, text='') my_label.grid(row=0, column=0) # Add a tkinter button widget, place it in the grid layout # and attach the change_text() function my_button = Button(window, text='Say Hi', width=10, command=change_text) my_button.grid(row=1, column=0) # Enter the main event loop window.mainloop() 32
My Application Say Hi Figure 5.01 A GUI application with a button
After running the code, press the ‘Say Hi’ button to see how this small application works. Notice how the button is linked to the change_text() function by command= in the button definition. FURTHER INFORMATION
The tkinter module provides classes, objects and methods that you can access and use in your own applications. Tkinter is written using object-oriented programming (OOP), which is beyond the scope of the syllabus. In OOP programs, object methods are accessed using the dot operator. This can be seen above in the change_text() function where the config() method is applied to the label widget. If you want to learn more about OOP you might like to work through Python: Building Big Apps, a level 3 book in the Coding Club series, or perhaps try Introduction to Programming with Greenfoot by Michael Kölling, which teaches Java programming in a very interactive, gamebased way. It is worth noting that while the syllabus focuses on solving problems through a top-down design process, discussed in detail in Chapter 8, OOP is a good example of how to solve problems through bottom-up design.