input: Write a function to reverse a given string. The function should return a new string with the characters of the input string in reverse order. If the input string is empty, the function should return an empty string.
  
  def reverse_string(input_string):
      return input_string[::-1]
  
  assert reverse_string("hello") == "olleh"
  assert reverse_string("Python") == "nohtyP"
  assert reverse_string("") == ""
output: def reverse_string(input_string):
      return input_string[::-1]