Sometimes I get MRO failures when defining classes. For example, if
R < E, C
B < S, E
S < C
Z < B, R
Then Z cannot be instantiated because C precedes E in B and E precedes C in R. The problem is that when the inheritance graph was topologically-sorted in B, the order was S, C, E. It could just as easily have been S, E, C. So, one solution is to add C explicitly to B's base class list, but this is annoying because B might not care about C (it's an implementation detail of S). It also means that if the hierarchy changes, a lot of these added extra base classes need to be fixed.
I propose adding a magic member to classes:
__precedes__ that is a list of classes. So, the fix for the above problem would be to define E as follows:
class E:
from whatever import C
__precedes__ = [C]
Then, when topologically-sorting (so-called linearizing) the ancestor classes, Python can try to ensure that E precedes C when defining B.