Python Interview Questions and Answers

 Python Interview Questions and Answers

What is Python?

Answer:
Python is a high-level, interpreted, object-oriented programming language known for its readability and simplicity. It supports multiple programming paradigms like procedural, object-oriented, and functional programming.

What are the key features of Python?

Answer:

  • Easy to learn and read

  • Interpreted language

  • Dynamically typed

  • Large standard library

  • Cross-platform support

  • Supports OOP and functional programming

What is the difference between list and tuple?

Answer:

List  Tuple
Mutable            Immutable
Uses []            Uses ()
Slower            Faster
Can be modified            Cannot be modified

Example:

my_list = [1, 2, 3]
my_tuple = (1, 2, 3)

What is the difference between == and is?

Answer:

  • == checks value equality

  • is checks memory location (identity)

Example:

a = [1,2]
b = [1,2]

print(a == b)  # True
print(a is b)  # False

What are Python data types?

Answer:

  • int

  • float

  • str

  • list

  • tuple

  • dict

  • set

  • bool

What is a decorator?

Answer:
A decorator is a function that modifies the behavior of another function without changing its code.

Example:

def decorator(func):
    def wrapper():
        print("Before function")
        func()
        print("After function")
    return wrapper

@decorator
def greet():
    print("Hello")

greet()

What is the difference between deepcopy and copy?

Answer:

  • copy() → Creates shallow copy (nested objects share reference)

  • deepcopy() → Creates complete independent copy

What is list comprehension?

Answer:
A concise way to create lists.

Example:

squares = [x**2 for x in range(5)]

What is a lambda function?

Answer:
An anonymous function defined using lambda.

Example:

add = lambda a, b: a + b
print(add(2, 3))

What is the difference between *args and **kwargs?

Answer:

  • *args → Pass multiple positional arguments

  • **kwargs → Pass multiple keyword arguments

Example:

def example(*args, **kwargs):
    print(args)
    print(kwargs)

What is GIL (Global Interpreter Lock)?

Answer:
GIL is a mutex in CPython that allows only one thread to execute Python bytecode at a time. It prevents true multi-threading in CPU-bound programs.

What are generators?

Answer:
Generators are functions that use yield to return values one at a time, saving memory.

Example:

def gen():
    yield 1
    yield 2

Difference between append() and extend()?

Answer:

  • append() → Adds single element

  • extend() → Adds multiple elements

What is exception handling?

Answer:
Handling runtime errors using try, except, finally.

Example:

try:
    x = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero")

What is the difference between @staticmethod and @classmethod?

Answer:

  • @staticmethod → No access to class or instance

  • @classmethod → Access to class using cls

What is Python’s memory management?

Answer:

  • Automatic memory allocation

  • Reference counting

  • Garbage collection

What are Python modules and packages?

Answer:

  • Module → A single Python file

  • Package → Collection of modules in a directory with __init__.py

What is monkey patching?

Answer:
Modifying a class or module at runtime.

What is the difference between multithreading and multiprocessing?

Answer:

  • Multithreading → Multiple threads, shared memory

  • Multiprocessing → Multiple processes, separate memory

What are common Python interview coding problems?

Answer:

  • Reverse a string

  • Check palindrome

  • Find prime number

  • Remove duplicates

  • Binary search

  • Anagram check

What will be the output?

a = [1, 2, 3]
b = a
b.append(4)
print(a)

Answer:
[1, 2, 3, 4]
Because b references the same list object as a.

What is the output?

print(0.1 + 0.2 == 0.3)

Answer:
False
Due to floating-point precision issues.

Mutable Default Argument Problem

def add_item(item, my_list=[]):
    my_list.append(item)
    return my_list

print(add_item(1))
print(add_item(2))

Answer:

[1]
[1, 2]

Default list is created only once, not every function call.

What will this print?

x = "Python"
print(x[::-1])

Answer:
nohtyP (String slicing reverse)

Output?

print(bool("False"))

Answer:
True
Any non-empty string is True.

Difference between is and == (Tricky Example)

a = 256
b = 256
print(a is b)

Answer:
True (Small integers are cached)

What happens here?

for i in range(3):
    print(i)
    i = 5

Answer:

0
1
2

Loop variable reassignment doesn’t affect iteration.

What is the output?

print([i*i for i in range(3)])

Answer:
[0, 1, 4]

What will this return?

def func():
    try:
        return 1
    finally:
        return 2

print(func())

Answer:
2
👉 finally overrides return.

What is the output?

a = [1, 2, 3]
print(a * 2)

Answer:
[1, 2, 3, 1, 2, 3]


Mutable Default Argument Trap

Question

What is the output?

def add_item(value, items=[]):
    items.append(value)
    return items

print(add_item(1))
print(add_item(2))
print(add_item(3))

Answer

[1]
[1, 2]
[1, 2, 3]

Explanation

Default arguments are evaluated only once at function definition time — not each call.

Correct Version

def add_item(value, items=None):
    if items is None:
        items = []
    items.append(value)
    return items

Late Binding Closure Problem

Question

funcs = []

for i in range(3):
    funcs.append(lambda: i)

print([f() for f in funcs])

 Answer

[2, 2, 2]

Why?

Lambdas capture variable by reference, not by value.

Fix

funcs.append(lambda i=i: i)

What Will This Print?

a = [1, 2, 3]
b = a[:]
b[0] = 100

print(a)

Answer

[1, 2, 3]

Explanation

Slicing creates a shallow copy.

Tricky finally Block

def test():
    try:
        return 10
    finally:
        return 20

print(test())

Answer

20

finally overrides the return from try.

Deep vs Shallow Copy (Important)

import copy

a = [[1,2],[3,4]]
b = copy.copy(a)

b[0][0] = 100

print(a)

 Answer

[[100, 2], [3, 4]]

Shallow copy copies outer list only.

Dictionary Default Value Trap

data = dict.fromkeys(["a", "b"], [])
data["a"].append(1)

print(data)

Answer

{'a': [1], 'b': [1]}

Both keys share same list reference.

Tricky Boolean Logic

print([] == False)
print(bool([]))

Answer

False
False

Empty list is False in boolean context but not equal to False.

Generator vs List (Memory Question)

gen = (x*x for x in range(5))
print(gen)

Answer

It prints a generator object, not values.

Use list(gen) to see values.

Class Variable vs Instance Variable

class Test:
    items = []
    
    def add(self, value):
        self.items.append(value)

a = Test()
b = Test()

a.add(1)
print(b.items)

Answer

[1]

Class variables are shared across instances.

 What is the Output?

print(0.1 + 0.2 == 0.3)

Answer

False

Floating point precision issue.

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