Arithmetic operator overloading in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of adding two custom objects with overloaded + operator

Consider the following Python class that overloads the + operator. What will be the output of the code below?

Python

class Number:
    def __init__(self, value):
        self.value = value
    def __add__(self, other):
        return Number(self.value + other.value)
    def __str__(self):
        return str(self.value)

n1 = Number(5)
n2 = Number(10)
result = n1 + n2
print(result)

A 15

B Number object at some memory address

C TypeError

D 510

💡 Hint

Look at how the __add__ method returns a new Number object and how __str__ controls printing.

The __add__ method returns a new Number object with the sum of the two values. The print calls __str__, which returns the string of the summed value, so it prints 15.

❓ Predict Output

intermediate

Output of subtracting custom objects with overloaded - operator

What is the output of this code that overloads the - operator?

Python

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __sub__(self, other):
        return Point(self.x - other.x, self.y - other.y)
    def __repr__(self):
        return f"Point({self.x}, {self.y})"

p1 = Point(10, 5)
p2 = Point(3, 2)
print(p1 - p2)

A Point(7, 3)

B Point(13, 7)

C TypeError

D None

💡 Hint

Check how the __sub__ method calculates the difference of coordinates.

The __sub__ method returns a new Point with each coordinate subtracted. So (10-3, 5-2) = (7, 3).

❓ Predict Output

advanced

Output of multiplying custom objects with overloaded * operator returning int

What will this code print? The * operator is overloaded to return an integer.

Python

class Vector:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __mul__(self, other):
        return self.x * other.x + self.y * other.y

v1 = Vector(2, 3)
v2 = Vector(4, 5)
print(v1 * v2)

A None

B Vector(8, 15)

C TypeError

D 23

💡 Hint

The * operator here calculates the dot product of two vectors.

The dot product is (2*4) + (3*5) = 8 + 15 = 23, so the code prints 23.

❓ Predict Output

advanced

Output of in-place addition with overloaded __iadd__ method

What is the output of this code that overloads the += operator?

Python

class Counter:
    def __init__(self, count=0):
        self.count = count
    def __iadd__(self, other):
        self.count += other.count
        return self
    def __str__(self):
        return str(self.count)

c1 = Counter(5)
c2 = Counter(10)
c1 += c2
print(c1)

A Counter object at some memory address

B 15

C TypeError

D 10

💡 Hint

The __iadd__ method modifies the object in place and returns it.

The += operator calls __iadd__, which adds the counts and returns the updated object. Printing calls __str__, so it prints 15.

🧠 Conceptual

expert

Behavior of unsupported arithmetic operator overloading

Given this class that only overloads __add__, what happens if you try to subtract two objects?

class MyNum:
    def __init__(self, val):
        self.val = val
    def __add__(self, other):
        return MyNum(self.val + other.val)

x = MyNum(5)
y = MyNum(3)
z = x - y

A Returns None

B Returns MyNum(2)

C Raises TypeError: unsupported operand type(s) for -: 'MyNum' and 'MyNum'

D Raises AttributeError

💡 Hint

Check what happens if an operator method is not defined for a class.

Since __sub__ is not defined, Python raises a TypeError saying the operator is unsupported for the given types.