TypeError when changing colors in pygame

Question

So I'm experimenting in pygame and wrote some code for a rectangle that slowly changes color

a = 4
b = 3
c = 2

#some irrelevant code later

    if color[0]+a < 255:
        color[0] += a
    else:
        a *= -1
    if color[1]+b < 255:
        color[1] += b
    else:
        b *= -1
    if color[2]+c < 255:
        color[2] += c
    else:
        c *= -1

a, b, and c as the speed of change for red, green, and, blue.

The problem is that for some reason it will give me a TypeError: Invalid color argument after a few seconds of the program running, usually when the color is very blue. I don't see any reason an invalid color argument would appear.

Answer 1

I would expect a ValueError instead of a TypeError , but it looks like what's happening is that if we take a = 4 and work with color[0]

• color[0] == 250, so gets changed to 254
• color[0] == 254, so stays the same, a gets changed to -4
• color[0] == 254, so gets changed to 250
• ... keeps substracting 4 ....

And I'm not sure -4 is a valid colour...

maybe look at using

>>> from itertools import izip, cycle
>>> a = range(0, 20, 4) + range(20, 0, -4)
>>> b = range(0, 20, 3) + range(20, 0, -3)
>>> c = range(0, 20, 2) + range(20, 0, -2)
>>> test = izip(cycle(a), cycle(b), cycle(c))
>>> for i in range(30):
    print next(test)

(0, 0, 0)
(4, 3, 2)
(8, 6, 4)
(12, 9, 6)
(16, 12, 8)
(20, 15, 10)
(16, 18, 12)
(12, 20, 14)
(8, 17, 16)
(4, 14, 18)
(0, 11, 20)
(4, 8, 18)
(8, 5, 16)
(12, 2, 14)
(16, 0, 12)
(20, 3, 10)
(16, 6, 8)
(12, 9, 6)
(8, 12, 4)
(4, 15, 2)
(0, 18, 0)
(4, 20, 2)
(8, 17, 4)
(12, 14, 6)
(16, 11, 8)
(20, 8, 10)
(16, 5, 12)
(12, 2, 14)
(8, 0, 16)
(4, 3, 18)

Answer 2

You are eventually getting to -ve colours. You reverse the direction if the colour gets too high, but not if the colour gets too low. Check to make sure it is also greater than 0.

if 0 < color[0]+a < 255:
    color[0] += a
else:
    a *= -1

Answer 3

Since you are getting a TypeError, somewhere else in your code (maybe far away from where the TypeError actually occurs!), you are redefining color . For example, something like

color = 'blue'

Answer 4

There is a Color class

from pygame.locals import Color

def color_rand(c):
    try:
        c.r += random.randint(0,10)
    except ValueError:
        c.r = 0

bg = Color(0,0,0)
bg = color_rand(bg)