docs: def save(self, output=None):
          """
          Save the database to a file. If ``output`` is not given, the ``dbfile``
          given in the constructor is used.
          """
          if output is None:
              if self.dbfile is None:
                  return
              output = self.dbfile
  
          with open(output, 'w') as f:
              f.write(self._dump())