input: Write a function to print the absolute difference between two given numbers. If both numbers are equal then return 0.
  def absolute_difference(a, b):
      return abs(a - b)
  
  assert absolute_difference(9, 5)==4
  assert absolute_difference(5, 9)==4
  assert absolute_difference(0, 0)==0
output: def absolute_difference(a, b):
      return abs(a - b)