input: Write a function to reverse the characters of a given string input. If the input string is empty, return an empty string.
  def reverse_string(input_string):
      return input_string[::-1] if input_string else ""
  
  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(input_string):
      return input_string[::-1] if input_string else ""