pygame CheckCollision

import pygame, sys


#        00000000001111111111222222222233333333334
#        01234567890123456789012345678901234567890
Stage =("        ################################################################",#0
        "#                                                              #",#1
        "#   ####       #      ##   ## #####  #  #  #  #  #  #  #  #    #",#2
        "#  #          # #     # # # # #      #  #  #  #  #  #  #  #    #",#3
        "#  #   ##    #####    #  #  # ##     #  #  #  #  #  #  #  #    #",#4
        "#  #    #   #     #   #     # #                                #",#5
        "#   ####   #       #  #     # #####  #  #  #  #  #  #  #  #    #",#6
        "#                                                              #",#7
        "################################################################",#8
        "#                                                              #",#9
        "#                                                              #",#0
        "#                                                              #",#1
        "#                                                              #",#2
        "#                                                              #",#3
        "#                                                              #",#4
        "#                                                              #",#5
        "#                                                              #",#6
        "#                                                              #",#7
        "#                                                              #",#8
        "#                                                              #",#9
        "#                                                              #",#0
        "#                                                              #",#1
        "#                                                              #",#2
        "#                                                              #",#3
        "#                                                              #",#4
        "#                                                              #",#5
        "#                                                              #",#6
        "#                                                              #",#7
        "#                                                              #",#8
        "#                                                              #",#9
        "#                                                              #",#0
        "#                                                              #",#1
        "#                                                              #",#2
        "#                                                              #",#3
        "#                                                              #",#4
        "#                                                              #",#5
        "#                                                              #",#6
        "#                                                              #",#7
        "#                                                              #",#8
        "#                                                              #",#9
        "#                                                              #",#0
        "#                                                              #",#1
        "################################################################",#2
        "#                                                              #",#3
        "########                                                       #",#4
        "#                                                              #",#5
        "#                                                              #",#6
        "################################################################")#7


#globaler:
BlockSize = 16
PlayerSize = 12
ScreenSize = (1024, 768)
FPS = 60
Gravity = 0.20
BackgroundColour = (255, 255, 255)#(red, green, blue) range: 0-255
BlockColor = (0, 0, 0)

print "Defining helperfunctions...."
def CheckCollision(x, y):
    global BlockSize, PlayerSize, Stage

    for x2, y2 in ((1,0), (0,1), (0,1), (1,0)):#Each corner of player:
        #if corner of player is within a solid in Stage[y][x]:
        if Stage[int(y - 1 + PlayerSize*y2) // BlockSize][int(x - 1 + PlayerSize*x2) // BlockSize] == "#":
            return True
        if Stage[int(y + 2 + PlayerSize*y2) // BlockSize][int(x + 2 + PlayerSize*x2) // BlockSize] == "#":
            return True
        if Stage[int(y + PlayerSize*y2) // BlockSize][int(x + 2 + PlayerSize*x2) // BlockSize] == "#":
            return True
    return False

print "Setting up playerobject..."
class Player:
    def __init__(self, x, y):
        self.x, self.y = float(x), float(y)
        self.Color = (255, 0, 127)#(red, green, blue) range: 0-255
        self.vspeed = 0.0
    def Step(self):
        global Gravity
        #Apply gravitation pull:
        if not CheckCollision(self.x, self.y+1):#if there is no ground beneath the player's feet:
            self.vspeed += Gravity
        else:
            self.vspeed = 0.0

        #Walk:
        Keys = pygame.key.get_pressed()
        if Keys[pygame.K_d] in (1,2):#Right D
            if not CheckCollision(self.x+1, self.y):
                self.x += 5
        if Keys[pygame.K_a] in (1,2):#Left A
            if not CheckCollision(self.x-1, self.y):
                self.x -= 5

        #jump:
        if Keys[pygame.K_w] in (1,2):#Up W
            #if ground beneath feet:
            if CheckCollision(self.x, self.y+1):
                self.vspeed = -6

        #add gravity and jump to self.y:
        if self.vspeed <> 0.0:
            #check if the fall will collide
            if CheckCollision(self.x, self.y+self.vspeed):
                #if so, step pixel by pixel until hitting the wall:
                for i in xrange(int(self.y), int(self.y+self.vspeed), 1 if self.vspeed > 0 else -1):
                    if CheckCollision(self.x, i):
                        self.y = float(i-1) if self.vspeed > 0 else float(i+1)
                        break
            else:
                self.y += self.vspeed

        print self.vspeed
    def Draw(self, Parent):
        global PlayerSize
        pygame.draw.rect(Parent, self.Color, (int(self.x), int(self.y), PlayerSize, PlayerSize))#(Surface, color, (x, y, width, height))
you = Player(1*BlockSize, 46*BlockSize)

print "Initalizing pygame..."
pygame.init()
Screen = pygame.display.set_mode(ScreenSize)
Timer = pygame.time.Clock()
#main loop:
print "START GAME!"
while 1:
    #maintain FPS:
    Timer.tick(FPS)

    #read input:
    for i in pygame.event.get():
        if i.type == pygame.QUIT:
            sys.exit()


    #step:
    you.Step()

    #draw:
    Screen.fill(BackgroundColour)#clear screen
    for x in xrange(len(Stage[0])):
        for y in xrange(len(Stage)):
            if Stage[y][x] == "#":
                pygame.draw.rect(Screen, BlockColor, (x*BlockSize, y*BlockSize, BlockSize, BlockSize))#(Surface, color, (x, y, width, height))
    you.Draw(Screen)

    #update changes done to Screen:
    pygame.display.flip()