Base Tornado handler with error catching

base_error_handler.py

class BaseErrorHandler(tornado.web.RequestHandler):
    """ catch exceptions and form error json response
        add traceback if need
    """
    def write_error(self, status_code, **kwargs):
        """ handle exception """
        self.add_header('Result', 'Error')
        if status_code == 500:
            exc_info = kwargs.get('exc_info')
            if exc_info:
                exc_type, exc_value, _ = exc_info
                tb = format_exception(*exc_info)
                msg = '%s: %s' % (exc_type.__name__, exc_value)
                resp = {'error': msg}
                if os.environ.get('KPI_DEBUG'):
                    resp['traceback'] = ''.join(tb)
                self.write(resp)
            else:
                self.write({'error': status_code})
        else:
            self.write({'error': status_code})