Question

I’m using Python 2.7 and Pygame 1.9.1
The fact that there are a few things that pygame and IDLE do not like each other is irrelevant as I attempted to run it as a .py file as well.

This works:

import pygame

y = 0
dir = 1
running = 1
width = 800
height = 600
screen = pygame.display.set_mode((width, height))
linecolor = 255, 0, 0
bgcolor = 0, 0, 0

while running:
    event = pygame.event.poll()
    if event.type == pygame.QUIT:
        running = 0

    screen.fill(bgcolor)
    pygame.draw.line(screen, linecolor, (0, y), (width-1, y))

    y += dir
    if y == 0 or y == height-1: dir *= -1

    pygame.display.flip()

But this does not work:

import pygame

y = 0
dir = 1
running = 1
width = 800
height = 600
linecolor = 255, 0, 0
bgcolor = 0, 0, 0
screen = pygame.display.set_mode((640, 400))


while running:
        event = pygame.event.poll()
        if event.type == pygame.QUIT:
            running = 0

        screen.fill(bgcolor)
        pygame.draw.aaline(screen, linecolor, (0, y), (width-1, y)

        y += dir
        if y == 0 or y == height-1: dir *= -1

        pygame.display.flip()

Could anybody explain the differences and why one works over the other?

The only diffrence appears to be the the two lines locations:

linecolor = 255, 0, 0

and

bgcolor = 0, 0, 0

Answer 1

But that’s not the only difference. This is a syntax error:

    pygame.draw.aaline(screen, linecolor, (0, y), (width-1, y)

It also differs from the above in that it calls aaline instead of line and is indented 8 spaces instead of 4. Any of these differences could be causing a problem (since the 8-space indention, to me, suggest a possible mix of tabs and spaces.)

Also, in general, it’s a good idea to post a stack trace when you get an error from a piece of code. They contain useful information.