Method overriding behavior in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is method overriding in Python?

Method overriding happens when a child class provides its own version of a method that already exists in its parent class. This new method replaces the parent's method when called on the child class object.

intermediate

How does Python decide which method to call when a method is overridden?

Python uses the method of the child class if it exists. If the child class does not have the method, Python looks up the parent class method. This is called dynamic method dispatch.

intermediate

Can a child class call the parent class's overridden method? How?

Yes, the child class can call the parent class's method using the super() function. For example, super().method_name() calls the parent method inside the child method.

beginner

What happens if the child class does not override a method from the parent class?

If the child class does not override the method, the method from the parent class is used when called on the child class object.

beginner

Why is method overriding useful in programming?

It allows child classes to customize or extend the behavior of parent classes without changing the parent code. This helps create flexible and reusable code.

What does method overriding allow a child class to do?

A Provide a new version of a method from the parent class

B Delete a method from the parent class

C Create a method with a different name

D Prevent the parent class from being used

Method overriding lets the child class provide its own version of a method that exists in the parent class.

How can a child class call the original method from its parent class after overriding it?

A It is not possible

B By renaming the method

C By deleting the child method

D Using the super() function

The super() function allows the child class to access the parent class's method even after overriding it.

If a method is not overridden in the child class, which method is called?

A An error occurs

B A random method

C The parent class method

D The child class method

If the child class does not override the method, the parent class's method is used.

What is the term for Python choosing which method to call at runtime?

A Static typing

B Dynamic method dispatch

C Method hiding

D Compile-time binding

Dynamic method dispatch means Python decides at runtime which method to call, especially with overridden methods.

Why is method overriding important in object-oriented programming?

A It allows customizing inherited behavior

B It prevents inheritance

C It deletes parent classes

D It creates new classes automatically

Method overriding lets child classes change or extend the behavior they inherit from parent classes.

Explain method overriding and how Python decides which method to run when a method is overridden.

Think about how child and parent classes interact when they have methods with the same name.

Describe how to call a parent class's method from a child class when the method is overridden.

Remember the special function that helps access parent methods.

Practice

1. What does method overriding allow a child class to do in Python?

easy

A. Prevent the parent class method from being used anywhere

B. Create a new method with a different name

C. Change the behavior of a method inherited from the parent class

D. Automatically call the parent class method without code

Solution

1. Step 1: Understand method overriding concept

   Method overriding means the child class provides its own version of a method that exists in the parent class.

2. Step 2: Identify what overriding changes

   The child class method replaces the parent's method behavior when called on the child instance.

3. Final Answer:

   Change the behavior of a method inherited from the parent class -> Option C

4. Quick Check:

   Method overriding = change inherited method behavior [OK]

Hint: Overriding means child changes parent's method behavior [OK]

Common Mistakes:

• Thinking overriding creates a new method with a different name
• Believing overriding disables parent method everywhere
• Assuming parent method is called automatically without super()

2. Which of the following is the correct way to override a method named greet in a child class?

easy

A. def greet(self, extra):\n print('Hello from child')

B. def greet(self):\n print('Hello from child')

C. def greet_child(self):\n print('Hello from child')

D. def greet():\n print('Hello from child')

Solution

1. Step 1: Match method name exactly

   Overriding requires the child method to have the same name as the parent method, here 'greet'.

2. Step 2: Check method signature

   The method must include 'self' as the first parameter to be a proper instance method.

3. Final Answer:

   def greet(self):\n print('Hello from child') -> Option B

4. Quick Check:

   Same name and self parameter = correct override [OK]

Hint: Override by matching method name and self parameter [OK]

Common Mistakes:

• Changing method name instead of overriding
• Omitting self parameter in method definition
• Adding extra parameters that don't match parent method

3. What will be the output of this code?

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

class Child(Parent):
    def greet(self):
        print('Hello from Child')

obj = Child()
obj.greet()

medium

A. Hello from Parent

B. Error: greet method not found

C. Hello from Parent\nHello from Child

D. Hello from Child

Solution

1. Step 1: Identify method overriding

   The Child class defines its own greet method, overriding Parent's greet.

2. Step 2: Determine which method is called

   Calling obj.greet() on a Child instance calls the Child's greet method, printing 'Hello from Child'.

3. Final Answer:

   Hello from Child -> Option D

4. Quick Check:

   Child method overrides Parent method = 'Hello from Child' [OK]

Hint: Child method runs when overridden, not parent's [OK]

Common Mistakes:

• Expecting both parent and child messages to print
• Thinking parent method runs instead of child
• Assuming error due to method name conflict

4. Find the error in this code that tries to override a method:

class Parent:
    def show(self):
        print('Parent show')

class Child(Parent):
    def show():
        print('Child show')

obj = Child()
obj.show()

medium

A. Missing self parameter in Child's show method

B. Parent class method show is private

C. Child class should not override show method

D. obj.show() should be called as Child.show(obj)

Solution

1. Step 1: Check method signature in Child class

   The Child's show method is missing the 'self' parameter, so it is not a proper instance method.

2. Step 2: Understand impact of missing self

   Calling obj.show() will cause a TypeError because Python expects the first argument (self) but none is defined.

3. Final Answer:

   Missing self parameter in Child's show method -> Option A

4. Quick Check:

   Instance methods must have self parameter [OK]

Hint: Instance methods always need self as first parameter [OK]

Common Mistakes:

• Ignoring missing self parameter
• Thinking method overriding is not allowed
• Believing calling method differently fixes error

5. Given this code, what will be the output?

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

class Child(Parent):
    def greet(self):
        super().greet()
        print('Hello from Child')

obj = Child()
obj.greet()

hard

A. Hello from Parent\nHello from Child

B. Hello from Child

C. Hello from Parent

D. Error: super() used incorrectly

Solution

1. Step 1: Understand super() call in Child's greet

   The Child's greet method calls super().greet(), which runs the Parent's greet method first.

2. Step 2: Follow the print statements

   First, 'Hello from Parent' is printed, then 'Hello from Child' is printed after.

3. Final Answer:

   Hello from Parent\nHello from Child -> Option A

4. Quick Check:

   super() calls parent method before child code [OK]

Hint: super() runs parent method before child code [OK]

Common Mistakes:

• Expecting only child's message to print
• Thinking super() causes error without arguments
• Ignoring order of print statements