Tetris Clone using Python & Pygame

import math, random, sys, time
import pygame
import pygame.gfxdraw
from pygame.locals import *

# define some colors
FUCHSIA = (255,   0, 255)
PURPLE  = (128,   0, 128)
TEAL    = (  0, 128, 128)
LIME    = (  0, 255,   0)
GREEN   = (  0, 128,   0)
OLIVE   = (128, 128,   0)
YELLOW  = (255, 255,   0)
ORANGE  = (255, 165,   0)
RED     = (255,   0,   0)
MAROON  = (128,   0,   0)
SILVER  = (192, 192, 192)
GREY    = (128, 128, 128)
NIGHT   = (32,   32,  32)
BLUE    = (  0,   0, 255)
NAVY    = (  0,   0, 128)
AQUA    = (  0, 255, 255)
WHITE   = (255, 255, 255)
BLACK   = (  0,   0,   0)

# define some data
BLOCKS = {1: {'startingY' : [0, 2, 0, 2], 'block' : [[(-1, 0), (0, 0), (1, 0), (2, 0)], [(1, -2), (1, -1), (1, 0), (1, 1)], [(-1, 0), (0, 0), (1, 0), (2, 0)], [(0, -2), (0, -1), (0, 0), (0, 1)]]}, # long one
          2: {'startingY' : [0, 1, 0, 1], 'block' : [[(-1, 0), (0, 0), (1, 0), (0, 1)], [(-1, 0), (0, -1), (0, 0), (0, 1)], [(0, 0), (-1, 1), (0, 1), (1, 1)], [(0, -1), (0, 0), (0, 1), (1, 0)]]}, # T shape
          3: {'startingY' : [0, 1, 0, 1], 'block' : [[(-1, 1), (-1, 0), (0, 0), (1, 0)], [(-1, -1), (0, -1), (0, 0), (0, 1)], [(1, 0), (-1, 1), (0, 1), (1, 1)], [(0, -1), (0, 0), (0, 1), (1, 1)]]}, # L left
          4: {'startingY' : [0, 1, 0, 1], 'block' : [[(-1, 0), (0, 0), (1, 0), (1, 1)], [(0, -1), (0, 0), (0, 1), (-1, 1)], [(-1, 0), (-1, 1), (0, 1), (1, 1)], [(0, -1), (0, 0), (0, 1), (1, -1)]]}, # L right
          5: {'startingY' : [0, 1, 0, 1], 'block' : [[(-1, 0), (0, 0), (0, 1), (1, 1)], [(1, -1), (1, 0), (0, 0), (0, 1)], [(-1, 0), (0, 0), (0, 1), (1, 1)], [(0, -1), (0, 0), (-1, 0), (-1, 1)]]}, # lightening 1
          6: {'startingY' : [0, 1, 0, 1], 'block' : [[(-1, 1), (0, 1), (0, 0), (1, 0)], [(0, -1), (0, 0), (1, 0), (1, 1)], [(-1, 1), (0, 1), (0, 0), (1, 0)], [(-1, -1), (-1, 0), (0, 0), (0, 1)]]}, # lightening 2
          7: {'startingY' : [1], 'block' : [[(-1, -1), (0, -1), (-1, 0), (0, 0)]]}, # square

          }

BLOCK_COLORS = [BLACK, RED, TEAL, ORANGE, NAVY, PURPLE, GREEN, YELLOW]

# exit the program
def quit():
    for event in pygame.event.get():
        if event.type == QUIT or (event.type == KEYDOWN and event.key == K_ESCAPE):
            return True
    return False

# draw a patterned title
class tiles:
    def __init__(self):
        global NIGHT, W, H

        self.tileSize = 32
        self.tile = pygame.Surface((self.tileSize, self.tileSize))

        for linePos in range(0, self.tileSize * 2, 8):
            pygame.draw.line(self.tile, NIGHT, (linePos, 0), (linePos - self.tileSize, self.tileSize), 1)

        #self.tile.convert()
        self.displayWidthInTiles = (W / self.tileSize) * self.tileSize
        if W % self.tileSize > 0: self.displayWidthInTiles += self.tileSize

        self.displayHeightInTiles = (H / self.tileSize) * self.tileSize
        if H % self.tileSize > 0: self.displayHeightInTiles += self.tileSize

        print self.displayWidthInTiles, self.displayHeightInTiles

    def fillDisplay(self, displaySurf):
        global AREAS, W, H
        for tilePosY in range(0, self.displayHeightInTiles, self.tileSize):
            for tilePosX in range(0, self.displayWidthInTiles, self.tileSize):
                displaySurf.blit(self.tile, (tilePosX, tilePosY))
        AREAS.append((0, 0, W, H))

class blockZone:
    def __init__(self):
        global BLOCKS, W, H

        #define the area in which the blocks fall and stack in
        self.height = (int(H * 0.9722222222222222) / 20) * 20
        self.topMargin = (H - self.height) / 2

        self.blockSize = int(float(self.height) / 20)

        self.width = self.blockSize * 10
        self.leftMargin = (W - self.width) / 2

        self.bzSurf = pygame.Surface((self.width, self.height))

        self.stack = [[0 for y in range(20)] for x in range(10)]

        self.currentBlock = random.randint(1, 7)
        self.rotation = 0
        self.blockPosX = 5
        self.blockPosY = BLOCKS[self.currentBlock]['startingY'][self.rotation]
        self.nextBlock = random.randint(1, 7)

    def blitToDisplay(self, displaySurf):
        global AREAS
        displaySurf.blit(self.bzSurf, (self.leftMargin, self.topMargin))
        AREAS.append((self.leftMargin, self.topMargin, self.width, self.height))

    def drawStack(self):
        global BLOCK_COLORS
        for x in range(10):
            for y in range(20):
                pygame.draw.rect(self.bzSurf, BLOCK_COLORS[self.stack[x][y]], (x * self.blockSize, y * self.blockSize, self.blockSize, self.blockSize), 0)

    def drawBlock(self, delete = False):
        global BLOCKS, BLOCK_COLORS

        block = BLOCKS[self.currentBlock]['block'][self.rotation]
        if delete:
            blockID = 0
        else:
            blockID = self.currentBlock

        for bit in block:
            y = self.blockPosY + bit[1]
            self.stack[self.blockPosX + bit[0]][y] = blockID

    def fall(self):
        global BLOCKS
        self.drawBlock(True)
        if self.collisionOnFall():
            self.drawBlock()
            self.currentBlock = self.nextBlock
            self.nextBlock = random.randint(1, 7)
            self.rotation = 0
            self.blockPosY = BLOCKS[self.currentBlock]['startingY'][0]
            self.blockPosX = 5
            self.drawBlock()
        else:
            self.blockPosY += 1
            self.drawBlock()

    def collisionOnFall(self):
        global BLOCKS
        block = BLOCKS[self.currentBlock]['block'][self.rotation]

        tempY = self.blockPosY + 1
        for bit in block:
            x = self.blockPosX + bit[0]
            y = tempY + bit[1]
            if y > 19: return True
            if self.stack[x][y] > 0: return True

        return False

    def collisionOnMove(self, rotate = True):
        global BLOCKS

        if rotate:
            block = BLOCKS[self.currentBlock]['block'][(self.rotation + 1) % len(BLOCKS[self.currentBlock]['block'])]
        else:
            block = BLOCKS[self.currentBlock]['block'][self.rotation]

        for bit in block:
            x = self.blockPosX + bit[0]
            y = self.blockPosY + bit[1]
            if x > 9 or x < 0 or y > 19 or y < 0: return True
            if self.stack[x][y] > 0: return True

        return False

    def rotateBlock(self):
        global BLOCKS
        if not self.collisionOnMove():
            self.rotation += 1
            self.rotation %= len(BLOCKS[self.currentBlock]['block'])

# define display surface
W, H = 1280, 720
HW, HH = W / 2, H / 2

# initialise display
pygame.init()
FONT = pygame.font.SysFont(None, 72)
DS = pygame.display.set_mode((W, H))
pygame.display.set_caption("Tetris Clone")
FPS = 1
SPF = 1.00 / FPS

# the areas of the display that need updating
AREAS = []

# create the background tiles instance
TILES = tiles()
TILES.fillDisplay(DS)

BZ = blockZone()
BZ.drawBlock()

# start FPS monitoring
FPSTime = time.time()

# monitor key held
keyHeld = False

# main loop
while not quit():
    k = pygame.key.get_pressed()

    if k[K_DOWN]:
        SPF = 1.00 / (FPS * 20)
    else:
        SPF = 1.00 / FPS

    if k[K_LEFT] and not keyHeld:
        BZ.drawBlock(True)
        BZ.blockPosX -= 1
        print BZ.blockPosX
        if BZ.collisionOnMove(False):
            BZ.blockPosX += 1
        BZ.drawBlock()

    if k[K_RIGHT] and not keyHeld:
        BZ.drawBlock(True)
        BZ.blockPosX += 1
        print BZ.blockPosX
        if BZ.collisionOnMove(False):
            BZ.blockPosX -= 1
        BZ.drawBlock()

    if k[K_UP] and not keyHeld:
        BZ.drawBlock(True)
        BZ.rotateBlock()
        BZ.drawBlock()

    if k[K_RETURN]:
        pygame.image.save(DS, "screenshot.png")
        pygame.quit()
        sys.exit()

    # when a key is pressed it has to be released and pressed again to repeat action
    if True in k[273:277]:
        keyHeld = True
    else:
        keyHeld = False


    BZ.drawStack()
    BZ.blitToDisplay(DS)

    if time.time() > FPSTime + SPF:
        # test for collision
        BZ.fall()
        FPSTime = time.time()

    pygame.display.update(AREAS)
    AREAS = []

    #DS.fill(BLACK)
pygame.quit()
sys.exit()