On Mon, Jul 19, 2010 at 9:33 AM, Phil Thompson <[email protected]> wrote: > On Sun, 18 Jul 2010 18:11:15 -0400, Darren Dale <[email protected]> > wrote: >> I am reading the dip documentation at >> > http://www.riverbankcomputing.co.uk/static/Docs/dip/complete_example.html >> , and have a question about the following: >> >> "dip will invoke an observe() handler when the value of an attribute >> is set, even if the new value is the same as the old one. We therefore >> use the _propagate_changes attribute to prevent possible recursion >> problems" >> >> Why is it necessary to invoke the observe handler when the value of an >> attribute does not change? There are quite a few infinite-recursion >> workarounds in the example. If the possibility of infinite recursion >> is so high, perhaps by default the handler should not be invoked if >> the attribute value does not change, unless observe() was called with >> a kwarg to invoke the handler regardless? > > Good question. > > The short answer is that it was easiest for me, but (obviously) what > matters is what's easier for developers using it.
Perhaps the example would be easier to understand (and to develop from scratch) with such a change. > The issue is to define what is meant by "changed", particularly when the > attribute is a class instance? Rebinding the attribute is obviously a > change, but what about a change to an attribute of the instance? The last example is another slightly different use case. The way enthought supports it is documented at http://code.enthought.com/projects/traits/docs/html/traits_user_manual/notification.html#example-of-a-dynamic-notification-handler . Darren _______________________________________________ PyQt mailing list [email protected] http://www.riverbankcomputing.com/mailman/listinfo/pyqt
