input: Write a function to optimize a given Python script that reverses a string.
  
  ### Function:
  def reverse_string(string):
      return string[::-1]
  
  ### Assertions:
  assert reverse_string("hello")=="olleh"
  assert reverse_string("Python")=="nohtyP"
  assert reverse_string("")==""
  assert reverse_string("12345")=="54321"
output: def reverse_string(string):
      return string[::-1]