code: def install_visa_handler(self, session, event_type, handler, user_handle=None):
          
          try:
              new_handler = self.install_handler(session, event_type, handler, user_handle)
          except TypeError as e:
              raise errors.VisaTypeError(str(e))
  
          self.handlers[session].append(new_handler + (event_type,))
          return new_handler[1]
docs: Installs handlers for event callbacks.
  
          :param session: Unique logical identifier to a session.
          :param event_type: Logical event identifier.
          :param handler: Interpreted as a valid reference to a handler to be installed by a client application.
          :param user_handle: A value specified by an application that can be used for identifying handlers
                              uniquely for an event type.
          :returns: user handle (a ctypes object)