Create a new Python source file and write the following code in it.

1  import pygame
2  import sys
3  
4  pygame.init()
5  bgcolor = (200, 200, 100)
6  surf = pygame.display.set_mode((400,400))
7
8  circle_color = (0, 255, 255)
9  x, y = 200, 300
10 circle_rad = 50
11 
12 pygame.display.set_caption("My Pygame Window")
13
14 while True:
15     for event in pygame.event.get():
16         if event.type == pygame.QUIT:
17             sys.exit()        
18         elif event.type == pygame.KEYDOWN:            
19             if event.key == pygame.K_UP:
20                 y -= 10
21             elif event.key == pygame.K_DOWN:
22                 y += 10
23             elif event.key == pygame.K_RIGHT:
24                 x += 10
25             elif event.key == pygame.K_LEFT:
26                 x -= 10
27                 
28     circle_pos = (x, y)            
29 	
30     surf.fill(bgcolor)
31     pygame.draw.circle(surf, circle_color , 
32                        circle_pos , circle_rad)
33     pygame.display.flip()

The first line imports the pygame package. On line 4, the modules within this pygame package are initialized. An instance of class Surface is created using display.set_mode method. This is the main PyGame window inside which the images will be drawn. To ensure that this window is constantly displayed on the screen, we need to add a while loop that will run forever, until the window is closed by the user. In this simple application everything we need is placed inside the while loop. The background color of the PyGame window represented by object surf is set on line 30.

A circular shape is drawn in the PyGame surface by the code on line 31. The arguments to draw.circle are (Surface, color, position, radius) . This creates a circle at the position specified by the argument circle_pos. The instance of class Surface is sent as the first argument to this method.

The code block 16-26 captures certain events. An event occurs when, for instance, a mouse button or a key is pressed. In this example, we instruct the program to do certain things when the arrow keys are pressed. When the RIGHT arrow key is pressed, the circle is drawn with the x coordinate offset by 10 pixels to the previous position. As a result, the circle appears to be moving towards right whenever you press the RIGHT arrow key. When the PyGame window is closed, the pygame.QUIT event occurs. Here, we simply exit the application by calling sys.exit() as done on line 17.

Finally, we need to ensure that everything drawn on the Surface is visible. This is accomplished by the code on line 31. If you disable this line, incompletely drawn images may appear on the screen.

Execute the program from a terminal window. It will show a new graphics window containing a circular shape. If you press the arrow keys on the keyboard, the circle will move in the direction indicated by the arrow key. The next illustration shows the screenshot of the original circle position (left) and when it is moved using the UP and RIGHT arrow keys.

A simple PyGame application with a circle drawn within the Surface (window). The image on the right side is a screenshot taken after maneuvering the position of the circle with the help of arrow keys: