A Boolean variable has only two possible values: True or False. It is common to use Booleans with control statements to determine the flow of a program. In this example, when the boolean value "x" is True, vertical black lines are drawn and when the boolean value "x" is False, horizontal gray lines are drawn.
b = False size(640, 360) background(0) stroke(255) d = 20 middle = width / 2 for i in range(d, width + d, d): if i < middle: b = True else: b = False ''' Analogous to the above is: b = i < middle Note: i < middle evaluates to a boolean True or False. ''' if b: # If b is True, run this block # Vertical line line(i, d, i, height - d) else: # Otherwise, if b is False, run this block # Horizontal line line(middle, i - middle + d, width - d, i - middle + d)