title: Python TypeError: bad operand type for unary -: 'tuple'
body: <p>I am trying to make a tetris game, but I don't understand this error?
  It seems to be line 34:</p>
  
  <pre><code>self.active_blk.move(-direction)
  </code></pre>
  
  <p>Here is my code:</p>
  
  <pre><code>import pygame
  import random
  from Block import Block
  
  class Stage():
  def __init__(self,cell_size,h_cells,v_cells):
      self.cell_size=cell_size
      self.width=h_cells
      self.height=v_cells
      self.blocks=[]
      self.active_blk=self.add_block()
  
  def add_block(self):
      blk=Block(0,self.cell_size,(random.randint(0,255),random.randint(0,255),random.randint(0,255)))
      self.blocks.append(blk)
      return blk
  
  def move_block(self,direction):
      self.active_blk.move(direction)
  
      obstacle=False
      for cell in self.active_blk.cells:
          if(cell.y&gt;=self.height or 
             cell.x&lt;0 or 
             cell.x&gt;= self.width): obstacle=True
  
      for blk in self.blocks:
          if(blk is self.active_blk): continue
          if(blk.collide_with(self.active_blk)):
              obstacle=True
              break;
  
      if(obstacle):
          self.active_blk.move(-direction)
  
  def draw(self,screen):
      screen.fill((0,0,0))  
      for blk in self.blocks:
          blk.draw(screen)
  </code></pre>