An Introduction to Python - Raspberry Pi User Guide - page 158

Continue the program with the following lines, paying attention to the indentation levels:
for event in pygame.event.get():
if event.type == QUIT:
pygame.quit()
sys.exit()
elif event.type == KEYDOWN:
he irst line, which comes right after the while loop begins, should be indented four spaces—
but it's a loop of its own, using a for instruction to check for pygame events like key presses. As a
result, the line under that needs to be indented an additional four spaces for a total of eight—but
that line, too, is a loop, using an if instruction to check whether the user has pressed a key. As a
result, the next line— pygame.quit() —is indented an additional four spaces for a total of 12
spaces. his logical progression of indentation tells Python where each loop begins and ends,
which is important: if the wrong number of spaces is used, the program won't work correctly. his
is why using a development environment like IDLE, which attempts to automatically indent code
where required, can be easier than using a plain text editor to create Python programs.
An if loop tells Python to check to see if a particular evaluation is true. he irst check, if
event.type == QUIT , tells Python to execute the indented code below if pygame reports
a QUIT message (which happens when the user presses the Escape key). he two lines
beneath that should be familiar from the gameOver function: they tell pygame and Python
to close down and exit.
he line beginning elif is used to extend if loops. Short for else if , an elif instruction is
evaluated when a previous if instruction was found to be false. In this case, the elif
instruction is used to see if pygame is reporting a KEYDOWN event, which is returned when
the user is pressing a key on the keyboard. As with the if instruction, code to be executed
when an elif is true should be indented by an additional four spaces plus whatever inden-
tation the elif instruction itself has. Type the following lines to give the elif instruction
something to do when the user presses a key:
if event.key == K_RIGHT or event.key == ord('d'):
changeDirection = 'right'
if event.key == K_LEFT or event.key == ord('a'):
changeDirection = 'left'
if event.key == K_UP or event.key == ord('w'):
changeDirection = 'up'
if event.key == K_DOWN or event.key == ord('s'):
changeDirection = 'down'
if event.key == K_ESCAPE:
pygame.event.post(pygame.event.Event(QUIT))