How does the order of mixins affect the derived class?
django, django-class-based-views, django-views, method-resolution-order, python
Solution
The MRO is basically depth-first, left-to-right. See Method Resolution Order (MRO) in new style Python classes for some more info.
You can look at the `__mro__` attribute of the class to check, but `FooMixin` should be first if you want to do "check A" first.
class UltimateBase(object):
def dispatch(self, *args, **kwargs):
print 'base dispatch'
class FooMixin(object):
def dispatch(self, *args, **kwargs):
print 'perform check A'
return super(FooMixin, self).dispatch(*args, **kwargs)
class BarMixin(object):
def dispatch(self, *args, **kwargs):
print 'perform check B'
return super(BarMixin, self).dispatch(*args, **kwargs)
class FooBar(FooMixin, BarMixin, UltimateBase):
pass
FooBar().dispatch()
Prints:
perform check A
perform check B
base dispatch
`View` has to be last so that it "catches" any attribute lookups that weren't on any mixins, without hiding any methods on those mixins. I'm not sure I understand that part of your question -- what it "why is it added at all" or "why is it added last"?
Problem
Say, I have the following mixins that overlaps with each other by touching `dispatch()`: ``` class FooMixin(object): def dispatch(self, *args, **kwargs): # perform check A ... return super(FooMixin, self).dispatch(*args, **kwargs) class BarMixin(object): def dispatch(self, *args, **kwargs): # perform check B ... return super(FooMixin, self).dispatch(*args, **kwargs) ``` If I want my view to go through the order, check A -> check B, should my code be `MyView(FooMixin, BarMixin, View)` or `MyView(BarMixin, FooMixin, View)`? And why do we always put `View` or its subclasses after mixins? (I have noticed this from reading the source code of the django generic views, but I don't know the rationale behind it, if any)