input: Write a function to optimize a given Python script that reverses a string.
  
  ### Input:
  def reverse_string(string):
      reversed_string = ""
      for char in string:
          reversed_string = char + reversed_string
      return reversed_string
  
  ### Output:
  def reverse_string(string):
      return string[::-1]
  assert reverse_string("hello")=="olleh"
  assert reverse_string("world")=="dlrow"
  assert reverse_string("python")=="nohtyp"
  assert reverse_string("")==""
output: def reverse_string(string):
      return string[::-1]