input: 
  def str_to_lower(string: str) -> str:
      """ Converts a given string to its lowercase version.
      
      >>> str_to_lower("Hello World!")
      'hello world!'
      >>> str_to_lower("PYTHON PROGRAMMING")
      'python programming'
      """
      new_string = ""
  
      for char in string:
          new_string += char.lower()
  
      return new_string
  
output:     new_string = ""
  
      for char in string:
          new_string += char.lower()
  
      return new_string