python - pygame stop sprites from overlapping -

i'm making top-down game in pygame, it's basic right , coding experience/skill limited, i'm aware code won't flawless. right have character, , spawned zombies chase after him, after while merge single sprite image, , can't figure out how stop it.

from guess i'm thinking should use loop check whether zombie colliding other zombies, don't know how it, or whether should done within zombie class.

the code of area zombie moving below, i'm not sure if code movement needs overhaul work, cause it's primitive movement code.

thanks guys,

alex

def update(self):     zx=self.rect.topleft[0]-player.rect[0]     zy=self.rect.topleft[1]-player.rect[1]     rads=math.atan2(-zy, zx)     rads %= 2*pi     angle = math.degrees(rads)     self.rimage=pygame.transform.rotate(self.image, angle-90)     size=self.rimage.get_size()      if self.damaged:         self.rimage=pygame.transform.rotate(self.image_damaged, angle-90)         screen.blit(self.rimage, (self.rect.topleft[0]-size[0]/2,self.rect.topleft[1]-size[1]/2))         print "oww"         self.damaged=false       if pygame.sprite.collide_circle(self, player):         self.collidenumber += 1     else:         self.collidenumber = 0      if self.collidenumber < 3:          if player.rect[0]<self.rect[0]:             self.rect[0]-=self.speed          if player.rect[0]>self.rect[0]:             self.rect[0]+=self.speed          if player.rect[1]<self.rect[1]:             self.rect[1]-=self.speed          if player.rect[1]>self.rect[1]:             self.rect[1]+=self.speedenter code here