After reading lesson 37, you’ll be able to
- Describe a graphical user interface
- Use a library for a graphical user interface to write a program
Every program you’ve written has interacted with the user in a text-based way. You’ve been displaying text on the screen and getting text input from the user. Although you can write interesting programs this way, the user is missing a more visual experience.
Consider this
Think about a program you use in your everyday life: a browser to go on the internet. What kinds of interactions do you have with the browser?
Answer: You open the browser window, click buttons, scroll, select text, and close the browser window.
Many programming languages have libraries that help programmers write visual applications. These applications use familiar interfaces between the user and the program: buttons, text boxes, drawing canvases, icons, and many more.
A library for a graphical user interface (GUI) is a set of classes and methods that know how to interface between the user and the operating system to display graphical control elements, called widgets. Widgets are meant to enhance the user experience through interaction: buttons, scrollbars, menus, windows, drawing canvases, progress bars, or dialog boxes are a few examples.
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Quick check 37.1
A canvas
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Listing 37.1. Creating a window
import tkinter #1
window = tkinter.Tk() #2
window.geometry("800x200") #3
window.title("My first GUI") #4
window.configure(background="grey") #5
window.mainloop() #6
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Quick check 37.2
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btn = tkinter.Button(window) btn.pack()
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Listing 37.2. Adding widgets to the window
import tkinter
window = tkinter.Tk()
window.geometry("800x200")
window.title("My first GUI")
window.configure(background="grey")
red = tkinter.Button(window, text="Red", bg="red") #1
red.pack() #2
yellow = tkinter.Button(window, text="Yellow", bg="yellow")
yellow.pack()
green = tkinter.Button(window, text="Green", bg="green")
green.pack()
textbox = tkinter.Entry(window) #3
textbox.pack() #3
colorlabel = tkinter.Label(window, height="10", width="10") #4
colorlabel.pack() #4
window.mainloop()
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Figure 37.2. Window after adding three buttons, one text box, and one label. The top button is red and is labeled Red, the middle button is yellow and is labeled Yellow, and the bottom button is green and is labeled Green.
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Table 37.1. Widgets available in tkinter
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Listing 37.3. Event handler for a button click
import tkinter
def change_color(): #1
window.configure(background="white") #2
window = tkinter.Tk()
window.geometry("800x200")
window.title("My first GUI")
window.configure(background="grey")
white = tkinter.Button(window, text="Click", command=change_color) #3
white.pack()
window.mainloop()
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Listing 37.4. Program that reads a text box and counts down that many seconds
import tkinter
import time
def countdown(): #1
countlabel.configure(background="white") #2
howlong = int(textbox.get()) #3
for i in range(howlong,0,-1): #4
countlabel.configure(text=i) #5
window.update() #6
time.sleep(1) #7
countlabel.configure(text="DONE!") #8
window = tkinter.Tk()
window.geometry("800x600")
window.title("My first GUI")
window.configure(background="grey")
lbl = tkinter.Label(window, text="How many seconds to count down?") #9
lbl.pack()
textbox = tkinter.Entry(window) #10
textbox.pack()
count = tkinter.Button(window, text="Countdown!", command=countdown) #11
count.pack()
countlabel = tkinter.Label(window, height="10", width="10") #12
countlabel.pack()
window.mainloop()
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In this lesson, my goal was to teach you how to use a graphical user interface library. The library contains classes and methods that help programmers manipulate graphical elements of the operating system. Here are the major takeaways:
- Your GUI program works inside a window.
- In the window, you can add graphical elements, called widgets.
- You can add functions that perform tasks when a user interacts with the widget.
Write a program that stores names, phone numbers, and emails of people in a phonebook. The window should have three text boxes for the name, phone, and email. Then it should have one button to add a contact, and one button to show all contacts. Finally, it should have a label. When the user clicks the Add button, the program reads the text boxes and stores the information. When the user clicks the Show button, it reads all the contacts stored and prints them on a label.