Multiple inheritance syntax in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is multiple inheritance in Python?

Multiple inheritance is a feature where a class can inherit attributes and methods from more than one parent class.

beginner

How do you define a class that inherits from two parent classes <code>Parent1</code> and <code>Parent2</code>?

You write: <br><code>class Child(Parent1, Parent2):</code><br>This means <code>Child</code> inherits from both <code>Parent1</code> and <code>Parent2</code>.

intermediate

What happens if both parent classes have a method with the same name?

Python uses the Method Resolution Order (MRO) to decide which method to call. It looks for the method in the first parent class listed, then the next, and so on.

beginner

Write a simple example of multiple inheritance with two parent classes A and B and a child class C.

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

class B:
    def greet(self):
        return "Hello from B"

class C(A, B):
    pass

c = C()
print(c.greet())  # Output: Hello from A

intermediate

Why should you be careful when using multiple inheritance?

Because it can make code harder to understand and debug, especially if parent classes have methods with the same name or complex relationships.

How do you declare a class Child that inherits from Parent1 and Parent2?

A class Child(Parent1, Parent2):

B class Child(Parent1 & Parent2):

C class Child inherits Parent1, Parent2:

D class Child : Parent1, Parent2

In Python, multiple inheritance is declared by listing parent classes separated by commas inside parentheses after the class name.

If both parents have a method named show(), which parent's method is called in class Child(Parent1, Parent2)?

A An error occurs

B Parent2's method

C Parent1's method

D Both methods are called

Python follows the Method Resolution Order (MRO) and calls the method from the first parent listed.

What does MRO stand for in Python multiple inheritance?

A Multiple Return Output

B Method Resolution Order

C Method Recursive Operation

D Multiple Reference Object

MRO means Method Resolution Order, which is the order Python uses to look for methods in parent classes.

Which of these is a risk of using multiple inheritance?

A You cannot use methods from parent classes

B It disables inheritance from single classes

C It slows down the program significantly

D Code can become confusing and hard to debug

Multiple inheritance can make code complex and harder to maintain if not used carefully.

What keyword is used to define a class in Python?

A class

B def

C function

D inherit

The keyword class is used to define a class in Python.

Explain how to write a Python class that inherits from two parent classes and how Python decides which parent method to use if both have the same method name.

Think about the order of parent classes and how Python searches for methods.

Describe one advantage and one disadvantage of using multiple inheritance in Python.

Consider how multiple inheritance helps and what problems it might cause.

Practice

1. What is the correct way to declare a class Child that inherits from two parent classes Parent1 and Parent2 in Python?

easy

A. class Child(Parent1, Parent2):

B. class Child(Parent1 & Parent2):

C. class Child inherits Parent1, Parent2:

D. class Child: Parent1, Parent2

Solution

1. Step 1: Understand Python class inheritance syntax

   In Python, to inherit from multiple classes, list them separated by commas inside parentheses after the class name.

2. Step 2: Match the syntax to the options

   class Child(Parent1, Parent2): uses the correct syntax: class Child(Parent1, Parent2):. Other options use invalid syntax.

3. Final Answer:

   class Child(Parent1, Parent2): -> Option A

4. Quick Check:

   Multiple inheritance syntax = class Child(Parent1, Parent2): [OK]

Hint: List parent classes separated by commas in parentheses [OK]

Common Mistakes:

• Using '&' instead of commas between parent classes
• Writing 'inherits' keyword like other languages
• Not using parentheses after class name

2. Which of the following is a syntax error when defining a class with multiple inheritance?

easy

A. class MyClass(): pass

B. class MyClass(Parent1, Parent2): pass

C. class MyClass(Parent1): pass

D. class MyClass(Parent1 Parent2): pass

Solution

1. Step 1: Check syntax for multiple inheritance

   Parent classes must be separated by commas inside parentheses.

2. Step 2: Identify the incorrect option

   class MyClass(Parent1 Parent2): pass misses the comma between Parent1 and Parent2, causing a syntax error.

3. Final Answer:

   class MyClass(Parent1 Parent2): pass -> Option D

4. Quick Check:

   Missing comma between parents = SyntaxError [OK]

Hint: Always separate parent classes with commas [OK]

Common Mistakes:

• Omitting commas between parent classes
• Leaving out parentheses entirely
• Using colons instead of commas

3. What will be the output of this code?

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

class B:
    def greet(self):
        return "Hello from B"

class C(A, B):
    pass

obj = C()
print(obj.greet())

medium

A. "Hello from A"

B. TypeError

C. AttributeError

D. "Hello from B"

Solution

1. Step 1: Understand method resolution order (MRO)

   Class C inherits from A first, then B. Python looks for methods in the order of parents listed.

2. Step 2: Determine which greet() is called

   Since A is first, C uses A's greet method, returning "Hello from A".

3. Final Answer:

   "Hello from A" -> Option A

4. Quick Check:

   MRO follows parent order = "Hello from A" [OK]

Hint: First parent class method is used in multiple inheritance [OK]

Common Mistakes:

• Assuming last parent class method is called
• Expecting an error due to multiple parents
• Confusing method names or forgetting MRO

4. Find the error in this multiple inheritance code:

class X:
    pass

class Y:
    pass

class Z(X Y):
    pass

medium

A. Missing colon after class name

B. Missing comma between parent classes

C. Parent classes must be in square brackets

D. Class Z cannot inherit from X and Y

Solution

1. Step 1: Check syntax for multiple inheritance

   Parent classes must be separated by commas inside parentheses.

2. Step 2: Identify the syntax error

   In class Z(X Y):, the comma between X and Y is missing, causing a syntax error.

3. Final Answer:

   Missing comma between parent classes -> Option B

4. Quick Check:

   Comma missing between parents = SyntaxError [OK]

Hint: Separate parent classes with commas inside parentheses [OK]

Common Mistakes:

• Forgetting commas between parent classes
• Using square brackets instead of parentheses
• Thinking multiple inheritance is not allowed

5. Given these classes:

class Alpha:
    def action(self):
        return "Alpha"

class Beta:
    def action(self):
        return "Beta"

class Gamma(Alpha, Beta):
    def action(self):
        return super().action() + " & Gamma"

class Delta(Gamma, Beta):
    pass

obj = Delta()
print(obj.action())

What is the output?

hard

A. "Beta & Gamma"

B. "Gamma"

C. "Alpha & Gamma"

D. AttributeError

Solution

1. Step 1: Understand the inheritance chain and MRO

   Delta inherits from Gamma and Beta. Gamma inherits from Alpha and Beta. The MRO for Delta is Delta, Gamma, Alpha, Beta, object.

2. Step 2: Trace the action() method call

   Delta uses Gamma's action(), which calls super().action(). In Gamma, super() refers to Alpha (next in MRO), so Alpha.action() returns "Alpha". Then Gamma appends " & Gamma".

3. Final Answer:

   "Alpha & Gamma" -> Option C

4. Quick Check:

   super() follows MRO = "Alpha & Gamma" [OK]

Hint: super() calls next in MRO, not just first parent [OK]

Common Mistakes:

• Assuming super() calls Beta's method instead of Alpha's
• Ignoring MRO order in multiple inheritance
• Expecting an error due to complex inheritance