code: def clean(self):
          
          super().clean()
  
          # At least a poster (user) or a session key must be associated with
          # the post.
          if self.poster is None and self.anonymous_key is None:
              raise ValidationError(
                  _('A user id or an anonymous key must be associated with a post.'),
              )
          if self.poster and self.anonymous_key:
              raise ValidationError(
                  _('A user id or an anonymous key must be associated with a post, but not both.'),
              )
  
          if self.anonymous_key and not self.username:
              raise ValidationError(_('A username must be specified if the poster is anonymous'))
docs: Validates the post instance.