How do I detect the collision of two sprites using pygame?

Question

This is my code so far, I can move and it places out a blip to pick up, I just need to know how to register that and move the blip to a new random spot! I am very new to pygame and not 100% fluent in python either, but I'm decent. If there are pdf:s good for intermediate coders when it comes to python that would be wonderful!

import sys, pygame, os, math
from random import randint

pygame.init()

size = width, height = 800, 600
speed = [2, 2]
black = 1, 1, 1
screen = pygame.display.set_mode(size)
pygame.display.set_caption('Pick up the squares!')
UP='up'
DOWN='down'
LEFT='left'
RIGHT='right'

ball = pygame.image.load("ball.png")
ballrect = ball.get_rect()
ballx = 400
bally = 300

blip = pygame.image.load("blip.png")
bliprect = blip.get_rect()
blipx = randint(1,800)
blipy = randint(1,600)

background = pygame.Surface(screen.get_size())
background = background.convert()

background.fill((250, 250, 250))


clock = pygame.time.Clock()

while 1:
    for event in pygame.event.get():
        if event.type == pygame.QUIT: sys.exit()


    keys = pygame.key.get_pressed()

    if keys[pygame.K_LEFT]:
        ballx  -= 5
    if keys[pygame.K_RIGHT]:
        ballx += 5
    if keys[pygame.K_UP]:
        bally -= 5
    if keys[pygame.K_DOWN]:
        bally +=5    

    screen.fill(black)
    screen.blit(ball, (ballx,bally))
    screen.blit(blip, (blipx, blipy))
    pygame.display.update()
    clock.tick(40)

Answer 1

Use the colliderect method of rectangles:

if ballrect.colliderect(bliprect):
    print 'Do something here'

Answer 2

A basic collision detection works like this (assuming you are working with two rectangles):

def does_collide(rect1, rect2):
    if rect1.x < rect2.x + rect2.width and rect1.x + rect1.width > rect2.x \ 
       and rect1.y < rect2.y + rect2.height and rect1.height + rect1.y > rect2.y:
        return True
    return False

Fortunately Pygame is packed with such methods, so you should go with @MalikBrahimi's answer - using colliderect function call, which will do the math for you.

Answer 3

You can also try using pygame.sprite.spritecollide():

if pygame.sprite.spritecollide(a, b, False):
    pass
    #Do something

a here is your variable name for the class for one of the sprites in the collision. b here is the group that your second sprite will be. You can set the last one to True, which will remove the sprite from the group. Setting to False will keep it the way it is. Here is an example:

if pygame.sprite.spritecollide(my_ball, ballGroup, False):
    Ball.speed[0] = -Ball.speed[0]
    hit.play()
Ball.move()

The variable name for my sprite is my_ball. The group containing the other sprite(s) in this collision is ballGroup. I set the last one to False to keep all the sprites on the surface. If I set to True, the sprite from ballGroup will be removed from the group and screen. I hope this helps you!