code: def versions(self, rev=None, index=None):
          
          raise NotImplementedError
          _revisions = [line.split()[0] for line in self.log.split('\n') if line]
          _versions = [Version(self.obj.repo.commit(r)) for r in _revisions if rev is None or r.startswith(rev)]
          if index is not None and len(_versions) > index:
              _versions = _versions[index]
          return _versions
docs: :return: List of Versions for this Item