python - Pygame key press event -

hey guys i'm trying add movement sprite have , i'm having trouble, heres code. i'm using wasd keys move player around place, can't seem figure out why won't move. appreciated.

import pygame import math  sys import exit pygame.locals import * pygame.mixer.init  class player(pygame.sprite.sprite):     def __init__(self, screen):         pygame.sprite.sprite.__init__(self)         self.image = pygame.image.load("ryu.png")         transcolor = self.image.get_at((1, 1))         self.image.set_colorkey(transcolor)         self.rect = self.image.get_rect()         self.dx = screen.get_width()/2         self.dy = screen.get_height()/2          self.rect.center = (self.dx, self.dy)         self.screen = screen         self.speed = 4          def update(self):             self.rect.center = (self.dx, self.dy)          def returnposition(self):             return self.rect.center         def moveleft(self):             if  self.rect.left < 0:                 self.dx+=0             else:                 self.dx-=self.speed          def moveright(self):             if self.rect.right >self.screen.get_width():                 self.dx+=0             else:                 self.dx+=self.speed          def moveup(self):             if self.rect.top <0:                 self.dy+=0             else:                 self.dy-=self.speed         def movedown(self):             if self.rect.bottom > self.screen.get_height():                 self.dy+=0             else:                 self.dy+=self.speed  def checkkeys(mydata):     (event, player) = mydata     keys = pygame.key.get_pressed()     if keys [k_a]:         print 'he turned left!!!'         player.moveleft()     if keys [k_s]:         print "he's going down!!!"     if keys [k_d]:         print "he turned right!!!"     if keys [k_w]:         print "he's going up!!!"  def main():     screen = pygame.display.set_mode((640, 480))     clock = pygame.time.clock()     keepgoing = true         pygame.display.set_caption("creating sprite")      player = player(screen)      background = pygame.surface(screen.get_size())     background.fill((0, 0, 0))      allsprites = pygame.sprite.group(player)      while keepgoing:         clock.tick(30)          event in pygame.event.get():             if event.type == pygame.quit:                 keepgoing = false          allsprites.clear(screen, background)         allsprites.update()         allsprites.draw(screen)         pygame.display.flip()  if __name__ == "__main__":     main()