Best practices for multiple inheritance in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method resolution order (MRO) in multiple inheritance

What is the output of this Python code showing the method resolution order (MRO) for classes with multiple inheritance?

Python

class A:
    pass

class B(A):
    pass

class C(A):
    pass

class D(B, C):
    pass

print(D.__mro__)

A (<class '__main__.D'>, <class '__main__.A'>, <class '__main__.B'>, <class '__main__.C'>, <class 'object'>)

B (<class '__main__.D'>, <class '__main__.C'>, <class '__main__.B'>, <class '__main__.A'>, <class 'object'>)

C (<class '__main__.D'>, <class '__main__.B'>, <class '__main__.C'>, <class '__main__.A'>, <class 'object'>)

D (<class '__main__.D'>, <class '__main__.B'>, <class '__main__.A'>, <class '__main__.C'>, <class 'object'>)

💡 Hint

Remember Python uses C3 linearization for MRO in multiple inheritance.

Python's MRO for class D with parents B and C is D, B, C, A, object. This order respects the inheritance hierarchy and avoids conflicts.

❓ Predict Output

intermediate

Output of method calls in diamond inheritance

What is the output of this code demonstrating method calls in diamond multiple inheritance?

Python

class A:
    def greet(self):
        return 'Hello from A'

class B(A):
    def greet(self):
        return 'Hello from B'

class C(A):
    def greet(self):
        return 'Hello from C'

class D(B, C):
    pass

obj = D()
print(obj.greet())

A Hello from D

B Hello from C

C Hello from A

D Hello from B

💡 Hint

Check which parent class appears first in the inheritance list of class D.

Class D inherits from B and C. Since B is first, its greet method is called due to Python's MRO.

🔧 Debug

advanced

Identify the error in multiple inheritance with conflicting methods

What error does this code raise when trying to create an instance of class D?

Python

class A:
    def action(self):
        return 'Action from A'

class B:
    def action(self):
        return 'Action from B'

class D(A, B):
    pass

obj = D()
print(obj.action())

A No error, output: Action from A

B No error, output: Action from B

C AttributeError: 'D' object has no attribute 'action'

D TypeError: Cannot create a consistent method resolution order (MRO) for bases A, B

💡 Hint

Check if the classes A and B have a common ancestor and how Python resolves method calls.

Python resolves method calls using MRO. Since A is first in inheritance, its action method is called without error.

📝 Syntax

advanced

Which option causes a syntax error in multiple inheritance?

Which of the following class definitions will cause a syntax error?

A

class D(A B):
    pass

B

class D(A, B):
    pass

C

class D(A, B):
    def method(self):
        pass

D

class D(A, B):
    def __init__(self):
        super().__init__()

💡 Hint

Check the syntax for listing multiple base classes in Python.

In Python, multiple base classes must be separated by commas. Missing comma causes syntax error.

🚀 Application

expert

Determine the final output with super() in multiple inheritance

What is the output of this code that uses super() in a multiple inheritance scenario?

Python

class A:
    def process(self):
        return 'A'

class B(A):
    def process(self):
        return super().process() + 'B'

class C(A):
    def process(self):
        return super().process() + 'C'

class D(B, C):
    def process(self):
        return super().process() + 'D'

obj = D()
print(obj.process())

A ABCD

B ACBD

C ABDC

D ACDB

💡 Hint

Trace the calls following Python's MRO and how super() delegates method calls.

The MRO is D, B, C, A, object. Each process calls super().process() adding its letter. So output is A + C + B + D = 'ACBD'.