code: def _convert_datetime_str(response):
      '''
      modify any key-value pair where value is a datetime object to a string.
      '''
      if response:
          return dict([(k, '{0}'.format(v)) if isinstance(v, datetime.date) else (k, v) for k, v in six.iteritems(response)])
      return Nonf _convert_datetime_str(response):
      '''
      modify any key-value pair where value is a datetime object to a string.
      '''
      if response:
          return dict([(k, '{0}'.format(v)) if isinstance(v, datetime.date) else (k, v) for k, v in six.iteritems(response)])
      return None
docs: modify any key-value pair where value is a datetime object to a string.