Adds content to the Dockerfile.

        :param input_str: Content.
        :type input_str: unicode | str

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'))