Steven D'Aprano wrote:
> These are not equivalent:
>
> B < S, E
> B < E, S
Not in general, but in many cases they will be, e.g. if
E and S have no method names in common. I think the OP is
implying that his case is one of those.
Maybe what's really wanted is a way to say "B inherits from
S and E, but it doesn't care what order they go in". Then
the MRO generating algorithm could in principle swap them
if it would result in a consistent MRO.
Interesting idea, but unfortunately, reordering base classes doesn't solve all of the problems that a precedence specification does. For example, the original example was:
R < E, C
B < S, E
S < C
Z < B, R
If we make it slightly more complicated:
class Y: pass
class X(Y): pass
class E(X): pass
class C: pass
class R(E, C): pass
class S(C, Y): pass
class B(S, E): pass
class Z(B, R): pass
Then, S and E can't be swapped.
Or maybe the MRO generator could decide for itself if the
order of two base classes can be swapped by inspecting
their attributes to see if any of them clash?
In general, I think that this would be a cool project, but is much hard than the user declaring a consistent order.
--
Greg
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