docs: def write(self, input_str):
          """
          Adds content to the Dockerfile.
  
          :param input_str: Content.
          :type input_str: unicode | str
          """
          self.check_not_finalized()
          if isinstance(input_str, six.binary_type):
              self.fileobj.write(input_str)
          else:
              self.fileobj.write(input_str.encode('utf-8'))