What causes the change in the method resolution order (MRO) in Python and why does it happen?

Changing the Method Resolution Order (MRO) in Python occurs when the class inheritance hierarchy is modified, especially when using multiple inheritance.

MRO determines the order in which Python searches for methods and attributes in classes during a call. Python 3 uses the C3 linearization algorithm, which guarantees a consistent and predictable order.

Reasons for changing the MRO:

• Adding or removing base classes.
• Changing the order of base classes in the inheritance list.

This is done to resolve conflicts in multiple inheritance and to ensure that each class appears in the MRO once and in the correct order.

For example:

class A: pass
class B(A): pass
class C(A): pass
class D(B, C): pass

print(D.__mro__)

Changing the order of base classes in class D(C, B): will change the MRO.