code: def _after(self, response):
          
          # Ignore excluded routes.
          if getattr(request, '_tracy_exclude', False):
              return response
  
          duration = None
          if getattr(request, '_tracy_start_time', None):
              duration = monotonic() - request._tracy_start_time
  
          # Add Trace_ID header.
          trace_id = None
          if getattr(request, '_tracy_id', None):
              trace_id = request._tracy_id
              response.headers[trace_header_id] = trace_id
  
          # Get the invoking client.
          trace_client = None
          if getattr(request, '_tracy_client', None):
              trace_client = request._tracy_client
  
          # Extra log kwargs.
          d = {'status_code': response.status_code,
               'url': request.base_url,
               'client_ip': request.remote_addr,
               'trace_name': trace_client,
               'trace_id': trace_id,
               'trace_duration': duration}
          logger.info(None, extra=d)
          return response
docs: Calculates the request duration, and adds a transaction
          ID to the header.