Method Resolution Order (MRO) in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the method resolution order of class C.

Python

class A:
    pass

class B:
    pass

class C(A, B):
    pass

print(C.[1]())

Drag options to blanks, or click blank then click option'

Amro

Border

Cmethods

Dresolution

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent method like 'order' or 'methods'.

Trying to access an attribute instead of calling a method.

The mro() method returns the method resolution order of a class.

2fill in blank

medium

Complete the code to define class C that inherits from classes A and B.

Python

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

class B:
    def greet(self):
        print('Hello from B')

class C([1]):
    pass

Drag options to blanks, or click blank then click option'

AA

BB, A

CA, B

DB

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing the order of classes.

Inheriting from only one class instead of both.

Class C inherits from A and B in that order, affecting the method resolution order.

3fill in blank

hard

Fix the error in the code to correctly call the greet method from class C.

Python

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

class B:
    def greet(self):
        print('Hello from B')

class C(A, B):
    pass

c = C()
c.[1]()

Drag options to blanks, or click blank then click option'

Agreet

Bgreeting

Chello

Dsay_hello

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that do not exist like 'hello' or 'say_hello'.

Trying to call an attribute instead of a method.

The method to call is greet, which is defined in classes A and B.

4fill in blank

hard

Fill both blanks to create a dictionary showing the MRO of class D and print it.

Python

class X:
    pass

class Y:
    pass

class D([1], [2]):
    pass

print(D.mro())

Drag options to blanks, or click blank then click option'

AX

BY

CA

DB

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated class names like A or B.

Reversing the order of inheritance.

Class D inherits from X and Y, so the MRO will reflect that order.

5fill in blank

hard

Fill all three blanks to create a class E that inherits from B and C, and print its MRO.

Python

class B:
    pass

class C:
    pass

class E([1], [2]):
    pass

print([3].mro())

Drag options to blanks, or click blank then click option'

AB

BC

CE

DD

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong class names in inheritance or print statement.

Forgetting to call the mro() method.

Class E inherits from B and C, and we print the MRO of E.

Practice

1. What does Method Resolution Order (MRO) in Python determine?

easy

A. The order Python compiles code

B. The order Python executes loops

C. The order Python looks for methods in inheritance

D. The order Python imports modules

Solution

1. Step 1: Understand MRO purpose

   MRO defines the sequence Python follows to find methods in classes with inheritance.

2. Step 2: Compare options

   Only The order Python looks for methods in inheritance correctly describes MRO's role in method lookup order.

3. Final Answer:

   The order Python looks for methods in inheritance -> Option C

4. Quick Check:

   MRO = method lookup order [OK]

Hint: MRO is about method search order in inheritance [OK]

Common Mistakes:

• Confusing MRO with loop or import order
• Thinking MRO controls code compilation
• Mixing MRO with unrelated Python features

2. Which of the following is the correct way to check the MRO of a class MyClass in Python?

easy

A. print(MyClass.__mro__)

B. print(MyClass.get_mro())

C. print(MyClass.MRO())

D. print(MyClass.mro)

Solution

1. Step 1: Recall MRO access methods

   Python provides __mro__ attribute and mro() method to check MRO.

2. Step 2: Identify correct syntax

   MyClass.__mro__ is a tuple showing MRO; MyClass.mro() is a method returning a list. print(MyClass.__mro__) uses __mro__ correctly with print.

3. Final Answer:

   print(MyClass.__mro__) -> Option A

4. Quick Check:

   Use __mro__ attribute to check MRO [OK]

Hint: Use ClassName.__mro__ to see MRO tuple [OK]

Common Mistakes:

• Using non-existent get_mro() method
• Forgetting parentheses for mro() method
• Trying to print mro without calling it

3. What will be the output of the following code?

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

print(D().greet())

medium

A. 'Hello from B'

B. 'Hello from A'

C. 'Hello from C'

D. Error: Ambiguous method

Solution

1. Step 1: Determine MRO of class D

   Class D inherits from B and C. Python uses C3 linearization: D > B > C > A.

2. Step 2: Find first greet method in MRO

   Method greet is found first in B, so D().greet() calls B's greet method.

3. Final Answer:

   'Hello from B' -> Option A

4. Quick Check:

   MRO order picks B's greet first [OK]

Hint: MRO checks parents left to right, first method wins [OK]

Common Mistakes:

• Assuming C's greet is called instead of B's
• Thinking A's greet is called directly
• Expecting an error due to multiple inheritance

4. Consider the following code snippet. What is the error and how to fix it?

class X:
    def method(self):
        return 'X'

class Y:
    def method(self):
        return 'Y'

class Z(X, Y):
    def method(self):
        return super().method()

print(Z().method())

medium

A. Error: super() call is ambiguous; fix by specifying class and self

B. Output: 'X' (no error)

C. Output: 'Y' (no error)

D. Error: Missing parentheses in print statement

Solution

1. Step 1: Analyze super() in Z.method()

   super() calls next method in MRO after Z, which is X.method().

2. Step 2: Check output of X.method()

   X.method() returns 'X', so print outputs 'X' with no error.

3. Final Answer:

   Output: 'X' (no error) -> Option B

4. Quick Check:

   super() calls next in MRO, here X.method() [OK]

Hint: super() calls next method in MRO automatically [OK]

Common Mistakes:

• Thinking super() needs explicit class and self
• Expecting output 'Y' instead of 'X'
• Assuming syntax error in print statement

5. Given the classes below, what is the MRO of class F?

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

hard

A. (F, E, D, B, C, A, object)

B. (F, D, E, B, C, A, object)

C. (F, D, B, C, E, C, B, A, object)

D. TypeError due to inconsistent MRO

Solution

1. Step 1: Understand MRO consistency rules

   Python requires MRO to be consistent and follow C3 linearization rules.

2. Step 2: Check classes D and E inheritance

   D inherits B then C; E inherits C then B. This creates conflicting order for F inheriting D and E.

3. Step 3: Result of conflict

   Python raises TypeError for class F due to inconsistent MRO from conflicting parent orders.

4. Final Answer:

   TypeError due to inconsistent MRO -> Option D

5. Quick Check:

   Conflicting parent order causes TypeError [OK]

Hint: Conflicting parent order causes MRO TypeError [OK]

Common Mistakes:

• Assuming Python picks one MRO silently
• Ignoring C3 linearization rules
• Trying to list MRO despite conflict