input: Write a function to optimize a given Python script that reverses a string. The function should be more efficient than the provided implementation.
  def reverse_string(string):
      return string[::-1]
  assert reverse_string("hello")=="olleh"
  assert reverse_string("Python")=="nohtyP"
  assert reverse_string("")==""
  assert reverse_string("12345")=="54321"
  assert reverse_string("racecar")=="racecar"
output: def reverse_string(string):
      return ''.join(reversed(string))