On Tue, 18 Nov 2014 00:00:42 -0700, Michael Torrie wrote: > On 11/17/2014 03:45 PM, Steven D'Aprano wrote: > >> Circular dependencies are not just a problem in Python, they are a >> problem throughout most of software design. > > Personally I find that duck typing eliminates a lot of the circular > dependency problems. Class A doesn't necessarily have to know about > Class B to work with instances of Class B. All that has to be known is > what methods are going to be available on those instances. The > interface pattern can help here if you wanted a bit more safety (like > what Zope provides). Either way it breaks up the dependency cycle > nicely. > > If Class A needs to instantiate instances of Class B (which depends on > Class A), then it could call a factory method to do so, perhaps set up > by a third party after both modules have been imported. > > There are lots of methods of avoiding the issue entirely. > > In the C or C++ world, I find that signalling frameworks can also be > used to break a dependency cycle. For example, if Class A needs to call > a method on an instance of Class B (which in turn depends on Class A), > that could be done instead as a signal, which is later connected to > Class B's method after everything is successfully instantiated. Also > makes testing a bit easier, because you can simply hook up the signals > to a test harness.
A bunch of useful thoughts. Thanks, folks! -- https://mail.python.org/mailman/listinfo/python-list
