<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def subject(self):
 """ Render the subject of the message to a string. """

        template_name = self.subject_template_name() if \
            callable(self.subject_template_name) \
            else self.subject_template_name
        subject = loader.render_to_string(
            template_name, self.get_context(), request=self.request
        )
        return ''.join(subject.splitlines())