def delete(self, doc):
        if doc.id is None:
            raise DatabaseException('Document does not have id')
        if doc.sid is None:
            try:
                rs = self.db.docs.remove({'id': doc.id}, safe=True)
                assert rs['n'] == 1
            except Exception as e:
                raise DatabaseException(e)
            return None
        doc.data = None
        return self.update(doc)
def _GetOutputStream(output_format, output_dir):
  assert output_format in _OUTPUT_FORMAT_CHOICES, 'Must specify a valid format.'
  assert output_format not in ('gtest', 'none'), (
      'Cannot set stream for \'gtest\' or \'none\' output formats.')

  if output_format == 'buildbot':
    return sys.stdout

  assert output_format in _OUTPUT_FILENAME_LOOKUP, (
      'No known filename for the \'%s\' output format' % output_format)
  output_file = os.path.join(output_dir, _OUTPUT_FILENAME_LOOKUP[output_format])
  open(output_file, 'a').close()  # Create file if it doesn't exist.
  return open(output_file, 'r+')