code: def proc_request(self, req):
          
  
          for idx in range(len(self)):
              resp = _safe_call(self[idx], 'proc_request', req)
  
              # Do we have a response?
              if resp is not None:
                  # Short-circuit
                  raise exc.ShortCircuit(self.proc_response(resp, idx - 1))
  
          # Return the request we were passed
          return req
docs: Pre-process a request through all processors in the stack, in
          order.  If any processor's proc_request() method returns a
          value other than None, that value is treated as a response and
          post-processed through the proc_response() methods of the
          processors preceding that processor in the stack.  (Note that
          the response returned this way is not passed to the
          processor's proc_response() method.)  Such a response will
          then be attached to a ShortCircuit exception.
  
          For convenience, returns the request passed to the method.