ThePythonBook/Assessment

Object-Oriented Programming Assessment

Test your understanding of Python classes, inheritance, magic methods, properties, dataclasses, composition, and polymorphism across 12 exercises.

Progress

1010 XP0/12

#1BankAccount Class

Write Code

Create a BankAccount class with:

__init__(self, owner: str, balance: float = 0) storing both as instance attributes

deposit(self, amount) that adds to balance and returns the new balance

withdraw(self, amount) that subtracts from balance only if sufficient funds exist, otherwise raises ValueError("Insufficient funds"); returns the new balance when successful

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#2Predict: Instance vs Class Attributes

Predict Output

What does this code print?

class Counter:
    count = 0

    def __init__(self):
        Counter.count += 1
        self.id = Counter.count

a = Counter()
b = Counter()
print(a.count, b.count, a.id, b.id)

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#3Fix: Inheritance and super()

Fix the Bug

The SavingsAccount should inherit from BankAccount and add an interest_rate. But the code crashes. Fix it so the tests pass.

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#4Magic Methods: __str__ and __repr__

Write Code

Create a Book class with:

__init__(self, title: str, author: str, pages: int)

__str__ returning "<title> by <author>"

__repr__ returning "Book('<title>', '<author>', <pages>)"

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#5Implement __add__ for Vector

Write Code

Create a Vector class representing a 2D vector:

__init__(self, x, y)

__add__(self, other) returning a new Vector with component-wise addition

__eq__(self, other) returning True if both components match

__repr__ returning "Vector(<x>, <y>)"

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#6Predict: super() and MRO

Predict Output

What does this code print?

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

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

class C(A):
    pass

class D(B, C):
    pass

d = D()
print(d.greet())
print(D.__mro__[1].__name__)

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#7Fix: Temperature Property

Fix the Bug

This Temperature class uses a property to convert between Celsius and Fahrenheit, but the property setter is broken. Fix the code so setting fahrenheit correctly updates the stored Celsius value.

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#8Refactor: Convert to Dataclass

Refactor

Refactor this class into a dataclass. The dataclass should automatically generate __init__, __repr__, and __eq__. Keep the full_name property.

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#9Composition: Engine and Car

Write Code

Implement two classes demonstrating composition:

Engine(horsepower: int) with a method start() returning "Engine (<hp>hp) started"

Car(make: str, engine: Engine) with a method start() returning "<make>: <engine.start()>"

The Car delegates to its Engine -- it does not inherit from it.

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#10Predict: Polymorphism with area()

Predict Output

What does this code print?

import math

class Circle:
    def __init__(self, r):
        self.r = r
    def area(self):
        return round(math.pi * self.r ** 2, 2)

class Rectangle:
    def __init__(self, w, h):
        self.w = w
        self.h = h
    def area(self):
        return self.w * self.h

shapes = [Circle(5), Rectangle(4, 6), Circle(1)]
print(sum(s.area() for s in shapes))

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#11Fix: __len__ and __eq__ for Playlist

Fix the Bug

This Playlist class has two bugs. len() returns the wrong value and equality comparison crashes. Fix both.

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#12Refactor: Extract a Shape Base Class

Refactor

The two shape classes share a duplicated describe() method. Refactor by:

1. Creating a Shape base class with describe(self) that returns "<class name>: area = <self.area()>"

2. Making Circle and Square inherit from Shape

3. Remove the duplicated describe methods from the subclasses

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