title: TypeError: argument 1 must be pygame.Surface, not type
body: <p>I'm making a submarine game in python, but when I try to run it, the interpreter gives me very strange error:
  "TypeError: argument 1 must be pygame.Surface, not type."
  I tried to search the web for my answer, but it seems like this isn't very usual error. I also tried to find error by myself, but everything   seemed fine to me. Here 's  part of the code that I think error is in:</p>
  
  <pre><code>mina = pygame.image.load('mina.png')
  class mina():
      def __init__(self, x , y):
          self.x = x
          self.y = y
          self.eksplozija = False
      def naris(self):
          screen.blit(mina, (self.x, self.y))
  igralec = podmornica(150, 300, 10)
  eksploziv = mina(700, 350)
  metki = []
  clock = pygame.time.Clock()
  def grafika():
      clock.tick(60)
      screen.blit(ozadje, (0,0))
      igralec.naris()
      #line, that doesn't work:
      eksploziv.naris()
      for metek in metki:
          metek.naris(screen)
      pygame.display.flip()
  </code></pre>