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Possible pitfalls — MRO inconsistency

MRO can report definition inconsistencies when a subtle change in the class D definition is introduced, which is possible when you work with complex class hierarchies.

Imagine that you have changed the class D definition from:

class D(B, C):
    pass

to:

class D(A, C):
    pass

Now when you run the code (the code is presented in the right pane, implement the change), you get:

Traceback (most recent call last):
  File "diamond.py", line 13, in 
    class D(A, C):
TypeError: Cannot create a consistent method resolution order (MRO) for bases A, C

output

This message informs us that the MRO algorithm had problems determining which method (originating from the A or C classes) should be called.

Possible pitfalls — MRO inconsistency

Code