Michael Foord wrote:
On 15/04/2011 02:02, Greg Ewing wrote:
Michael Foord wrote:
What I was suggesting is that a method not calling super shouldn't stop a *sibling* method being called, but could still prevent the *parent* method being called. There isn't necessarily a clear distinction between parents and siblings.
class A: ...
class B(A): ...
class C(A, B): ...
In C, is A a parent of B or a sibling of B?
Its neither, as C can't exist:
class A: pass ... class B(A): pass ... class C(A,B):pass ... Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: Cannot create a consistent method resolution order (MRO) for bases B, A
For a super call in C, B is a sibling to A. For a super call in B, A is a parent.
With the semantics I was suggesting if C calls super, but A doesn't then B would still get called.
A class cannot precede any of its sub-classes in an MRO, see http://en.wikipedia.org/wiki/C3_linearization If A is a "parent" (super-class) of B, then B must precede A in any MRO that contains them both. "Siblings", in the context of a single MRO are thus classes between which there is no sub-class/super-class relation. Mark.