On Mon, Sep 7, 2009 at 3:30 PM, Carl Banks<pavlovevide...@gmail.com> wrote: > > That's not what you did in your original post, though. > > Mixins should be listed first among bases, which is how you did it in > your original post, and how it had to be in order for it to "just > work" as I claimed. > > class FooX(MyMixin, BaseA) > class FooY(MyMixin, BaseB) > class FooZ(MyMixin, BaseC) > > > > If you are concerned that a base class might not define method_x (and > therefore that the super call from MyMixin would fail), then there are > a couple things you can do. First thing is to consider whether you > ought to be using two method instead of one. > > Otherwise the easiest thing is to catch and ignore AttributeError from > MyMixin's method_x: > > class MyMixin(object): > def method_x(self, a, b, c): > try: > f = super(MyMixin, self).method_x > except AttributeError: > pass > else: > f(a,b,c) > > Note that you don't want to call the super inside the try block > otherwise you risk catching spurrious AttributeErrors. > > This strategy might hide some typo-style errors with the base class, > so if you're worried about that, another strategy would be to define > another mixin which provides an empty method_x: > > class ProvideMethodX(self): > def method_x(self, a, b, c): > pass > > Then if BaseB does not define method_x, derive FooY from it like this: > > class FooY(MyMixin,ProvideMethodX,BaseB) > > Finally (and probably least confusingly) you could use separate mixins > for bases that define method_x and those that don't. > > > Carl Banks > -- > http://mail.python.org/mailman/listinfo/python-list >
I was trying to adapt Ryles' code into my existing example. I did what I thought Ryles did, but it didn't seem to work. I also tried flipping the order of the parents, as you suggested, but that didn't seem to change anything; it gives the same error. Also, there is no fear that one of the bases will not define method_x. The current API *requires* that all bases (MyMixin, BaseA, etc.) define a method_x, so if it does not exist for a base class, the developer isn't following the instructions. ;) -- http://mail.python.org/mailman/listinfo/python-list
