Magic Methods & Advanced OOP — Python Questions with Answers

Q1. easy

What are 'magic methods' (dunder methods)?

1. A Methods with double underscores (__str__, __len__...) that hook your class into Python's built-in behavior
2. B Methods that run magically fast
3. C Hidden methods you can't call
4. D Deprecated Python 2 methods

Q2. easy

Which method controls what print(obj) displays?

class Book:
    def __init__(self, title):
        self.title = title
    def __str__(self):
        return f"Book: {self.title}"

print(Book("Dune"))   # Book: Dune

1. A __str__
2. B __print__
3. C __show__
4. D __display__

Q21. easy

str(obj) and f"{obj}" both call which method?

1. A __str__
2. B __format__ only
3. C __text__
4. D __value__

Q27. easy

dir(obj) is useful because it...

print(dir([]))
# [..., 'append', 'clear', 'copy', 'count', ...]

1. A Lists all attributes and methods of the object - including inherited and dunder ones
2. B Shows the object's folder on disk
3. C Deletes the object
4. D Sorts the object

Q4. medium

Which method makes len(obj) work for your class?

class Cart:
    def __init__(self):
        self.items = []
    def __len__(self):
        return len(self.items)

print(len(Cart()))   # 0

1. A __len__
2. B __size__
3. C __count__
4. D length()

Q5. medium

Which method makes == compare your objects by CONTENT?

class Point:
    def __init__(self, x, y):
        self.x, self.y = x, y
    def __eq__(self, other):
        return self.x == other.x and self.y == other.y

print(Point(1, 2) == Point(1, 2))   # True

1. A __eq__
2. B __equals__
3. C __compare__
4. D __is__

Q6. medium

Which method lets you write v1 + v2 for your own Vector class?

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

v = Vector(1, 2) + Vector(3, 4)
print(v.x, v.y)   # 4 6

1. A __add__
2. B __plus__
3. C __sum__
4. D add()

Q8. medium

Which method makes square brackets work: playlist[0]?

class Playlist:
    def __init__(self, songs):
        self.songs = songs
    def __getitem__(self, i):
        return self.songs[i]

p = Playlist(["a", "b"])
print(p[1])          # b
for song in p: ...    # even iteration works!

1. A __getitem__
2. B __index__
3. C __bracket__
4. D __at__

Q9. medium

Which method powers 'x in obj'?

class Playlist:
    def __contains__(self, song):
        return song in self.songs

1. A __contains__
2. B __in__
3. C __has__
4. D __member__

Q11. medium

What does a SINGLE leading underscore mean: self._balance?

class Account:
    def __init__(self):
        self._balance = 0   # internal by convention

1. A A convention: 'internal - please don't touch from outside' (not enforced)
2. B Truly private - Python blocks access
3. C A syntax error
4. D The attribute is constant

Q15. medium

What is a @staticmethod?

class MathUtils:
    @staticmethod
    def add(a, b):        # no self!
        return a + b

print(MathUtils.add(2, 3))   # 5

1. A A method that gets NO automatic self/cls - a plain function stored in the class for organization
2. B A method that can't be changed
3. C A method shared with other classes
4. D A method that runs at import

Q19. medium

Which method decides your object's truthiness in 'if obj:'?

class Cart:
    def __init__(self):
        self.items = []
    def __len__(self):
        return len(self.items)

if not Cart():
    print("empty cart")   # prints!

1. A __bool__ (falling back to __len__ != 0 if absent)
2. B __true__
3. C __if__
4. D Objects are always False

Q20. medium

Why is c.area (a @property) better Python style than c.get_area()?

1. A Attribute syntax is cleaner, and you can start as a plain attribute and add logic later WITHOUT breaking callers
2. B get_ methods are illegal
3. C Properties are faster
4. D No reason - Java style is preferred

Q23. medium

Does Python have truly PRIVATE attributes like Java's private keyword?

1. A No - only conventions (_x) and name mangling (__x); everything remains reachable
2. B Yes - the private keyword
3. C Yes - via @private
4. D Only in classes marked sealed

Q24. medium

Trace: class Money: def __init__(self, amt): self.amt = amt def __add__(self, other): return Money(self.amt + other.amt) def __str__(self): return f"Rs.{self.amt}" print(Money(100) + Money(50))

1. A Rs.150
2. B 150
3. C Money(150)
4. D Error

Q26. medium

Which dunder pair powers the WITH statement (context managers)?

class Timer:
    def __enter__(self):
        self.start = time.time()
        return self
    def __exit__(self, *args):
        print(f"took {time.time() - self.start:.2f}s")

with Timer():
    do_work()

1. A __enter__ and __exit__
2. B __open__ and __close__
3. C __start__ and __stop__
4. D __with__ and __without__

Q29. medium

What does @dataclass (from dataclasses) generate for you?

from dataclasses import dataclass

@dataclass
class Point:
    x: int
    y: int

p = Point(1, 2)
print(p)               # Point(x=1, y=2)
print(p == Point(1, 2))  # True

1. A __init__, __repr__ and __eq__ automatically from the declared fields
2. B A database table
3. C Only documentation
4. D Getters and setters

Q30. medium

Why define __repr__ on every class you debug often?

def __repr__(self):
    return f"Order(id={self.id}, status={self.status!r})"

1. A Debuggers, logs, lists and the REPL all show __repr__ - a good one makes object state visible at a glance
2. B Python requires it
3. C It speeds up the class
4. D It enables inheritance

Q3. hard

What is the difference between __str__ and __repr__?

class Book:
    def __repr__(self):
        return f"Book({self.title!r})"

books = [Book("Dune")]
print(books)   # [Book('Dune')] - repr used inside lists!

1. A __str__ is the friendly display for users; __repr__ is the unambiguous version for developers/debugging (shown in the REPL and inside lists)
2. B They are interchangeable aliases
3. C __repr__ repeats the string twice
4. D __str__ is Python 2 only

Q7. hard

What does defining __lt__ (less-than) unlock for your class?

class Student:
    def __init__(self, marks):
        self.marks = marks
    def __lt__(self, other):
        return self.marks < other.marks

print(sorted([Student(90), Student(70)])[0].marks)  # 70

1. A The < operator AND sorting: sorted() can order your objects
2. B Only printing
3. C Nothing without __gt__ too
4. D Subtraction

Q10. hard

What does __call__ do? class Greeter: def __call__(self, name): return f"Hi {name}" g = Greeter() print(g("Ana"))

1. A Makes INSTANCES callable like functions - g("Ana") works, printing Hi Ana
2. B Calls the constructor again
3. C It's an error - objects can't be called
4. D Renames the object

Q12. hard

What does a DOUBLE leading underscore do: self.__secret?

class Account:
    def __init__(self):
        self.__pin = 1234

a = Account()
# a.__pin              # AttributeError
print(a._Account__pin)  # 1234 - mangled name

1. A Name mangling - Python renames it to _ClassName__secret, making accidental outside access harder
2. B Makes it 100% inaccessible
3. C Deletes it after __init__
4. D Nothing different from one underscore

Q13. hard

What does @property do? class Circle: @property def area(self): return 3.14 * self.r ** 2

c = Circle()
c.r = 2
print(c.area)    # 12.56 - no () needed

1. A Lets you access area WITHOUT parentheses - c.area - computed fresh each time like an attribute
2. B Caches the value forever
3. C Makes area static
4. D Prints the area

Q14. hard

How do you add validation when SETTING obj.age = value?

class Person:
    @property
    def age(self):
        return self._age
    @age.setter
    def age(self, value):
        if value < 0:
            raise ValueError("age can't be negative")
        self._age = value

1. A Define @property for age plus an @age.setter method that checks the value before storing
2. B Python can't intercept assignment
3. C Override __init__ only
4. D Use a global validator

Q16. hard

What does @classmethod receive instead of self?

class Date:
    def __init__(self, d, m, y):
        self.d, self.m, self.y = d, m, y
    @classmethod
    def from_string(cls, text):     # 'Date' arrives as cls
        d, m, y = map(int, text.split("-"))
        return cls(d, m, y)          # builds the instance

date = Date.from_string("03-07-2026")

1. A cls - the CLASS itself, so it can read class attributes or build instances
2. B Nothing at all
3. C A copy of every instance
4. D The parent class

Q17. hard

staticmethod vs classmethod vs normal method - which first argument does each receive?

1. A normal: self (the instance); classmethod: cls (the class); staticmethod: nothing automatic
2. B All three receive self
3. C normal: cls; classmethod: self; staticmethod: both
4. D They're interchangeable

Q18. hard

What is the true division of labor between __new__ and __init__?

1. A __new__ CREATES the object; __init__ then INITIALIZES the already-created object
2. B __init__ creates, __new__ initializes
3. C They are aliases
4. D __new__ is Python 2 only

Q22. hard

print([Book("Dune")]) shows <Book object at 0x...> even though Book defines __str__. Why?

class Book:
    def __repr__(self):
        return f"Book({self.title!r})"
print([Book("Dune")])   # [Book('Dune')]

1. A Containers display their items using __repr__, not __str__ - define __repr__ too
2. B Lists erase methods
3. C __str__ has a typo
4. D print can't handle lists

Q25. hard

v * 3 works on your Vector but 3 * v fails. Which method fixes the reversed order?

class Vector:
    def __mul__(self, n):
        return Vector(self.x * n, self.y * n)
    __rmul__ = __mul__     # 3 * v now works too

1. A __rmul__
2. B __mul2__
3. C __xmul__
4. D It cannot be fixed

Q28. hard

What is a SINGLETON, and which method is typically overridden to make one?

class Config:
    _instance = None
    def __new__(cls):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
        return cls._instance

print(Config() is Config())   # True

1. A A class allowing only ONE instance ever - override __new__ to return the same stored instance
2. B A class with one method - override __init__
3. C A single-file module
4. D An unmarried class