input: Write a function to reverse a given list.
  def reverse_list(list): 
      return list[::-1]
  assert reverse_list([1,2,3,4,5])==[5,4,3,2,1]
  assert reverse_list([5,3,7,1,9])==[9,1,7,3,5]
  assert reverse_list([])==[]
output: def reverse_list(list): 
      return list[::-1]