Modifying object state in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean to modify an object's state in Python?

Modifying an object's state means changing the values stored in its attributes. It's like updating the details of a real-world object, such as changing the color of a car or the balance in a bank account.

beginner

How do you change an attribute value of an object in Python?

You access the attribute using dot notation and assign a new value. For example, if you have an object 'car' with attribute 'color', you can write: car.color = 'red' to change its color.

intermediate

Why is it useful to have methods that modify an object's state?

Methods that modify state help keep changes organized and controlled. They can check if new values are valid before changing attributes, like making sure a bank account balance never goes negative.

intermediate

What is the difference between modifying an object's state and reassigning the object variable?

Modifying state changes the data inside the object without creating a new object. Reassigning the variable makes it point to a completely new object. Modifying keeps the same object identity.

beginner

Example: Given a class BankAccount with attribute balance, how would you add a method to deposit money?

You define a method like this:

    def deposit(self, amount):
        if amount > 0:
            self.balance += amount

This method changes the balance attribute by adding the deposit amount.

What does self.balance = 100 do inside a method?

A Creates a new variable named balance

B Sets the object's balance attribute to 100

C Deletes the balance attribute

D Calls a function named balance

Using self.balance = 100 sets or updates the balance attribute of the current object.

Which of these changes the state of an object?

A Assigning a new value to an attribute like <code>obj.name = 'Alice'</code>

B Creating a new object and assigning it to a variable

C Printing the object's attributes

D Calling a method that only returns a value without changing attributes

Changing an attribute value directly modifies the object's state.

Why might you use a method to change an attribute instead of changing it directly?

A To hide the attribute completely

B To make the program slower

C To check if the new value is valid before changing

D To avoid using the <code>self</code> keyword

Methods can include checks to ensure the new value is acceptable, preventing errors.

What happens if you reassign an object variable to a new object?

A The variable points to the new object, old object stays unchanged

B The old object is deleted immediately

C The old object's attributes are changed

D The program crashes

Reassigning changes the variable to refer to a new object; the old object remains unless no references point to it.

In a class, which keyword refers to the current object inside a method?

A obj

B this

C current

D self

In Python, self is used inside methods to refer to the current object.

Explain how you can change the state of an object in Python and why it is useful.

Think about updating details of something you own, like changing your phone's wallpaper.

Describe the difference between modifying an object's state and assigning a new object to a variable.

Consider the difference between repainting a car and buying a new car.