code: def set_default_subject(self, subject):
          
          if not (
              isinstance(subject, Subject)
              or isinstance(subject, (int, str,))
          ):
              raise TypeError
          if isinstance(subject, Subject):
              _subject_id = subject.id
          else:
              _subject_id = str(subject)
  
          self.http_post(
              '{}/links/default_subject'.format(self.id),
              json={'default_subject': _subject_id},
          )
docs: Sets the subject's location media URL as a link.
          It displays as the default subject on PFE.
  
          - **subject** can be a single :py:class:`.Subject` instance or a single
            subject ID.
  
          Examples::
  
              collection.set_default_subject(1234)
              collection.set_default_subject(Subject(1234))