```"""
Use sprites to pick up blocks

Sample Python/Pygame Programs
Simpson College Computer Science
http://simpson.edu/computer-science/

Explanation video: http://youtu.be/iwLj7iJCFQM
"""
import pygame
import random

# Define some colors
BLACK = (0, 0, 0)
WHITE = (255, 255, 255)
RED = (255, 0, 0)

class Block(pygame.sprite.Sprite):
"""
This class represents the block to be picked up.
It derives from the "Sprite" class in Pygame.
"""

def __init__(self, color, width, height):
""" Constructor. Pass in the color of the block,
and its x and y position. """

# Call the parent class (Sprite) constructor
super().__init__()

# Create an image of the block, and fill it with a color.
# This could also be an image loaded from the disk.
self.image = pygame.Surface([width, height])
self.image.fill(color)

# Fetch the rectangle object that has the dimensions of the image
# image.
# Update the position of this object by setting the values
# of rect.x and rect.y
self.rect = self.image.get_rect()

class Player(Block):
""" This class represents the player. It derives from block and thus gets
the same ___init___ method we defined above. """

# List of all the blocks we are carrying
carry_block_list = []

def update(self):
""" Method called when updating a sprite. """

# Get the current mouse position. This returns the position
# as a list of two numbers.
pos = pygame.mouse.get_pos()

# Now see how the mouse position is different from the current
# player position. (How far did we move?)
diff_x = self.rect.x - pos[0]
diff_y = self.rect.y - pos[1]

# Loop through each block that we are carrying and adjust
# it by the amount we moved.
for block in self.carry_block_list:
block.rect.x -= diff_x
block.rect.y -= diff_y

# Now wet the player object to the mouse location
self.rect.x = pos[0]
self.rect.y = pos[1]

# Initialize Pygame
pygame.init()

# Set the height and width of the screen
screen_width = 700
screen_height = 400
screen = pygame.display.set_mode([screen_width, screen_height])

# This is a list of 'sprites.' Each block in the program is
# added to this list. The list is managed by a class called 'Group.'
block_list = pygame.sprite.Group()

# This is a list of every sprite.
# All blocks and the player block as well.
all_sprites_list = pygame.sprite.Group()

for i in range(50):
# This represents a block
block = Block(BLACK, 20, 15)

# Set a random location for the block
block.rect.x = random.randrange(screen_width)
block.rect.y = random.randrange(screen_height)

# Add the block to the list of objects

# Create a RED player block
player = Player(RED, 20, 15)

# Loop until the user clicks the close button.
done = False

# Used to manage how fast the screen updates
clock = pygame.time.Clock()

# Hide the mouse cursor
pygame.mouse.set_visible(False)

# -------- Main Program Loop -----------
while not done:
for event in pygame.event.get():
if event.type == pygame.QUIT:
done = True

elif event.type == pygame.MOUSEBUTTONDOWN:
# When the mouse button is pressed, see if we are in contact with
# other sprites:
blocks_hit_list = pygame.sprite.spritecollide(player, block_list, False)

# Set the list of blocks we are in contact with as the list of
# blocks being carried.
player.carry_block_list = blocks_hit_list

elif event.type == pygame.MOUSEBUTTONUP:
# When we let up on the mouse, set the list of blocks we are
# carrying as empty.
player.carry_block_list = []

all_sprites_list.update()

# Clear the screen
screen.fill(WHITE)

# Draw all the spites
all_sprites_list.draw(screen)

# Limit to 60 frames per second
clock.tick(60)

# Go ahead and update the screen with what we've drawn.
pygame.display.flip()

pygame.quit()

```
﻿