input: Write a function to optimize a given Python script that reverses a string. The function should return a more efficient version of the reverse function.
  assert reverse_string("hello")=="olleh"
  assert reverse_string("python")=="nohtyp"
  assert reverse_string("")==""
  assert reverse_string("12345")=="54321"
  assert reverse_string("a")=="a"
output: def reverse_string(s):
      return s[::-1]