api.py 文件源码

def listens_for(target, identifier, *args, **kw):
    """Decorate a function as a listener for the given target + identifier.

    e.g.::

        from sqlalchemy import event
        from sqlalchemy.schema import UniqueConstraint

        @event.listens_for(UniqueConstraint, "after_parent_attach")
        def unique_constraint_name(const, table):
            const.name = "uq_%s_%s" % (
                table.name,
                list(const.columns)[0].name
            )

    A given function can also be invoked for only the first invocation
    of the event using the ``once`` argument::

        @event.listens_for(Mapper, "before_configure", once=True)
        def on_config():
            do_config()


    .. versionadded:: 0.9.4 Added ``once=True`` to :func:`.event.listen`
       and :func:`.event.listens_for`.

    .. seealso::

        :func:`.listen` - general description of event listening

    """
    def decorate(fn):
        listen(target, identifier, fn, *args, **kw)
        return fn
    return decorate