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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def __format_error(self, error_list_tag):
 """Format this error into a JSON response. Args: error_list_tag: A string specifying the name of the tag to use for the error list. Returns: A dict containing the reformatted JSON error response. """

    error = {'domain': self.domain(),
             'reason': self.reason(),
             'message': self.message()}
    error.update(self.extra_fields() or {})
    return {'error': {error_list_tag: [error],
                      'code': self.status_code(),
                      'message': self.message()}}