input: def str_to_lower(string: str) -> str:
      """ Convert a given string to its lowercase version.
      >>> str_to_lower("Hello World!")
      'hello world!'
      >>> str_to_lower("I AM LEARNING Python")
      'i am learning python'
      """
      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