[Python-Dev] Things to Know About Super

[M.-A. Lemburg]

On 2008-08-27 09:54, Greg Ewing wrote:
> Do you have a real-life example of this where multiple
> inheritance is actually used?
> 
> A non-contrived example or two would be a good thing to
> have in tutorials etc. where super() is discussed. It
> would help to convey the kinds of situations in which
> use of super() is and is not appropriate.

The typical use is in mixin classes that can be used to
add functionality to base classes, something you often find
in application frameworks, e.g.

class NewComponent(Feature1Mixin, Feature2Mixin, BaseComponent):
   ...

If the mixin classes have to override one of the methods defined
in BaseComponent, then they must pay attention to all other mixin
classes used to define the NewComponent.

Without super() (or some other mechanism of accessing the base
method, like e.g. mxTools' basemethod() for classic classes), the
mixins could potentially override methods defined by other mixin
classes which would then not get called.

As example, think of a typical application server method

def process_request(self, request):
    ...

To work properly, each implementation of the method in the mixin classes
and base class will have to be called - in the order they were defined
in the class definition.

-- 
Marc-Andre Lemburg
eGenix.com

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