def exchangeRowAndColumn(A,x,y):
# @param A: Picture;
# @param x: int; column number
# @param y: int; row number
  if getWidth(A) != getHeight(A) or x >= getWidth(A) or y >= getHeight(A) or x<0 or y<0:
    print "Error in parameter settings"
    return

  for i in range(0,getWidth(A)):
      px_1 = getPixel(A,x,i)
      px_2 = getPixel(A,i,y)
      color_1 = getColor(px_1)
      color_2 = getColor(px_2)
      setColor(px_1,color_2)
      setColor(px_2,color_1)
  repaint(A)