Method append

lib/sqlalchemy/orm/events.py:2546–2595

Receive a collection append event. The append event is invoked for each element as it is appended to the collection. This occurs for single-item appends as well as for a "bulk replace" operation. :param target: the object instance receiving the event. If

(
        self,
        target: _O,
        value: _T,
        initiator: Event,
        *,
        key: EventConstants = NO_KEY,
    )

                    mgr[target.key].dispatch._active_history = True

    def append(
        self,
        target: _O,
        value: _T,
        initiator: Event,
        *,
        key: EventConstants = NO_KEY,
    ) -> Optional[_T]:
        """Receive a collection append event.

        The append event is invoked for each element as it is appended
        to the collection.  This occurs for single-item appends as well
        as for a "bulk replace" operation.

        :param target: the object instance receiving the event.
          If the listener is registered with ``raw=True``, this will
          be the :class:`.InstanceState` object.
        :param value: the value being appended.  If this listener
          is registered with ``retval=True``, the listener
          function must return this value, or a new value which
          replaces it.
        :param initiator: An instance of :class:`.attributes.Event`
          representing the initiation of the event.  May be modified
          from its original value by backref handlers in order to control
          chained event propagation, as well as be inspected for information
          about the source of the event.
        :param key: When the event is established using the
         :paramref:`.AttributeEvents.include_key` parameter set to
         True, this will be the key used in the operation, such as
         ``collection[some_key_or_index] = value``.
         The parameter is not passed
         to the event at all if the the
         :paramref:`.AttributeEvents.include_key`
         was not used to set up the event; this is to allow backwards
         compatibility with existing event handlers that don't include the
         ``key`` parameter.

         .. versionadded:: 2.0

        :return: if the event was registered with ``retval=True``,
         the given value, or a new effective value, should be returned.

        .. seealso::

            :class:`.AttributeEvents` - background on listener options such
            as propagation to subclasses.

            :meth:`.AttributeEvents.bulk_replace`

        """

    def append_wo_mutation(
        self,