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Python Interview Questions and Answers

1. What is Python?

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

2. What are Python's key features?

Easy to learn and use
Interpreted language
Dynamically typed
Extensive standard library
Open-source and community-supported
Supports multiple paradigms
Platform-independent

3. What is PEP 8?

PEP 8 is Python’s style guide that provides best practices for writing clean, readable, and consistent code.

4. What is the difference between a list and a tuple?

List: Mutable (can be changed), uses []
Tuple: Immutable (cannot be changed), uses ()

5. What is the difference between Python 2 and Python 3?

Python 3 supports Unicode by default, uses print() as a function, and has improved syntax and standard library.

6. How is memory managed in Python?

Python uses automatic memory management, including garbage collection, reference counting, and a private heap.

7. What are Python’s data types?

Numeric types: int, float, complex
Sequence types: list, tuple, range
Text type: str
Set types: set, frozenset
Mapping type: dict
Boolean type: bool
Binary types: bytes, bytearray, memoryview

8. What are Python's built-in data structures?

List, Tuple, Dictionary, Set

9. What is the difference between is and ==?

is checks object identity (same memory location).
== checks value equality.

10. What are Python functions?

Functions are reusable blocks of code that perform specific tasks. Defined using def.

11. What is the difference between deepcopy() and copy()?

copy.copy() creates a shallow copy (references nested objects).
copy.deepcopy() creates a deep copy (completely independent clone).

12. What is a lambda function?

A small anonymous function defined using lambda keyword.

add = lambda x, y: x + y print(add(3, 4)) # Output: 7

13. What are Python decorators?

Functions that modify the behavior of other functions without modifying their code.

def decorator(func): def wrapper(): print("Before function call") func() print("After function call") return wrapper @decorator def say_hello(): print("Hello") say_hello()

14. What are *args and kwargs in Python?

args: Allows passing a variable number of positional arguments.
kwargs: Allows passing a variable number of keyword arguments.

def example(*args, **kwargs): print(args, kwargs) example(1, 2, 3, name="Alice", age=25)

15. What is the difference between a module and a package?

Module: A .py file containing Python code.
Package: A collection of modules, containing an __init__.py file.

16. What is the difference between @staticmethod, @classmethod, and instance methods?

Instance method: Works with instance (self).
Class method: Uses @classmethod, takes cls as the first parameter.
Static method: Uses @staticmethod, doesn’t take self or cls

17. How does exception handling work in Python?
try: x = 1 / 0 except ZeroDivisionError as e: print(f"Error: {e}") finally: print("Execution completed")

18. What are Python’s file handling modes?

"r" – Read
"w" – Write (overwrite)
"a" – Append
"rb"/"wb" – Binary read/write

19. What is list comprehension?
numbers = [x**2 for x in range(10) if x % 2 == 0] print(numbers) # [0, 4, 16, 36, 64]

20. How do you implement multithreading in Python?
import threading def print_numbers(): for i in range(5): print(i) thread = threading.Thread(target=print_numbers) thread.start()

1. What is the difference between shallow copy and deep copy?

A shallow copy creates a new object but does not copy nested objects; instead, it references them.
A deep copy creates a completely independent copy, including nested objects.

Example:

import copy list1 = [[1, 2, 3], [4, 5, 6]] shallow = copy.copy(list1) deep = copy.deepcopy(list1) shallow[0][0] = 100 print(list1) # [[100, 2, 3], [4, 5, 6]] (changes reflected) print(deep) # [[1, 2, 3], [4, 5, 6]] (no changes)

2. What is the difference between staticmethod and classmethod?

@staticmethod does not require self or cls and behaves like a regular function within a class.
@classmethod requires cls as the first parameter and can modify class variables.

Example:

class Example: class_var = 10 @staticmethod def static_method(): print("Static method called") @classmethod def class_method(cls): cls.class_var += 1 print("Class method called", cls.class_var) Example.static_method() # Output: Static method called Example.class_method() # Output: Class method called 11

3. What is the difference between generators and iterators?

Iterator: Implements __iter__() and __next__() and maintains state.
Generator: Uses yield to produce values lazily.

Example:

def gen_example(): for i in range(3): yield i gen = gen_example() print(next(gen)) # 0 print(next(gen)) # 1

4. What are Python’s memory management techniques?

Garbage Collection: Python uses automatic garbage collection.
Reference Counting: When an object’s reference count reaches zero, it is deleted.
Generational Garbage Collector: Objects are classified into generations and cleaned accordingly.

5. What is the Global Interpreter Lock (GIL)?

The GIL ensures that only one thread executes Python bytecode at a time, preventing true parallelism.
This affects multi-threading performance for CPU-bound tasks but not for I/O-bound tasks.

Example:

import threading def task(): for _ in range(1000000): pass t1 = threading.Thread(target=task) t2 = threading.Thread(target=task) t1.start() t2.start() t1.join() t2.join()

(Threads will not run truly in parallel due to GIL.)

6. How do you handle circular imports in Python?

Use import inside a function or import specific attributes to break circular dependencies.

Example:

# module1.py import module2 def func1(): module2.func2() # module2.py import module1 def func2(): module1.func1()

(Solution: Import within a function.)

7. What is the difference between is and ==?

is checks object identity (memory address).
== checks value equality.

a = [1, 2, 3] b = a c = [1, 2, 3] print(a is b) # True (same memory) print(a is c) # False (different objects) print(a == c) # True (same value)

8. What is the difference between del, remove(), and pop()?

del: Deletes an element by index or deletes the whole object.
remove(): Removes the first occurrence of a specific value.
pop(): Removes an element by index and returns it.

Example:

my_list = [1, 2, 3, 4] del my_list[1] # Deletes index 1 my_list.remove(3) # Removes value 3 x = my_list.pop(0) # Removes index 0 and returns it

9. What is the difference between map(), filter(), and reduce()?

map(): Applies a function to all elements.
filter(): Filters elements based on a function.
reduce(): Aggregates elements into a single result.

Example:

from functools import reduce nums = [1, 2, 3, 4] squares = list(map(lambda x: x**2, nums)) # [1, 4, 9, 16] evens = list(filter(lambda x: x % 2 == 0, nums)) # [2, 4] product = reduce(lambda x, y: x * y, nums) # 24

10. What is monkey patching in Python?

Monkey patching is modifying or extending a module or class at runtime.

Example:

class Example: def greet(self): print("Hello") def new_greet(self): print("Hi!") Example.greet = new_greet obj = Example() obj.greet() # Hi!

11. What are Python’s built-in hashable and unhashable types?

Hashable: int, float, str, tuple (immutable types).
Unhashable: list, dict, set (mutable types).

print(hash("hello")) # Valid print(hash((1, 2, 3))) # Valid # print(hash([1, 2, 3])) # TypeError: unhashable type: 'list'

12. How can you improve performance in Python?

Use generators instead of lists (yield).
Use built-in functions like sum(), max(), etc.
Use Cython, PyPy, or multiprocessing for performance.
Avoid global variables and unnecessary loops.

13. What is the difference between repr() and str()?

str() is user-friendly (used for display).
repr() is meant for debugging and development.

class Example: def __repr__(self): return "Example()" def __str__(self): return "This is an example" obj = Example() print(str(obj)) # This is an example print(repr(obj)) # Example()

14. How do you merge two dictionaries in Python?

dict1 = {"a": 1, "b": 2} dict2 = {"b": 3, "c": 4} # Method 1: Using `update()` dict1.update(dict2) # {'a': 1, 'b': 3, 'c': 4} # Method 2: Using dictionary unpacking merged = {**dict1, **dict2} # {'a': 1, 'b': 3, 'c': 4}

15. How does Python’s __call__ method work?

It allows an instance of a class to be called as a function.

class CallableClass: def __call__(self, x): return x * 2 obj = CallableClass() print(obj(5)) # 10

1. What are metaclasses in Python?

A metaclass is a class that defines how other classes behave.
Classes are instances of metaclasses.
The default metaclass in Python is type.

Example:

class Meta(type): def __new__(cls, name, bases, attrs): print(f"Creating class {name}") return super().__new__(cls, name, bases, attrs) class Example(metaclass=Meta): pass # Output: Creating class Example

2. What is the difference between deepcopy() and copy()?

copy() creates a shallow copy (references nested objects).
deepcopy() creates a full independent copy.

Example:

import copy list1 = [[1, 2], [3, 4]] shallow = copy.copy(list1) deep = copy.deepcopy(list1) shallow[0][0] = 100 print(list1) # [[100, 2], [3, 4]] (shallow copy modified) print(deep) # [[1, 2], [3, 4]] (deep copy remains unchanged)

3. How does Python handle memory management?

Reference Counting: Objects are deleted when their reference count reaches zero.
Garbage Collection: Python’s GC runs periodically to remove cyclic references.
Generational GC: Objects are divided into generations (young, middle-aged, old) for optimized cleanup.

Example:

import sys a = [1, 2, 3] print(sys.getrefcount(a)) # Output: 2 (1 for variable 'a', 1 for function argument)

4. How does the __slots__ attribute improve performance?

__slots__ prevents dynamic attribute creation and reduces memory usage.

Example:

class Example: __slots__ = ['a', 'b'] obj = Example() obj.a = 10 # obj.c = 20 # AttributeError: 'Example' object has no attribute 'c'

5. What is the difference between staticmethod, classmethod, and instance methods?

Instance Method: Works with self.
Class Method: Works with cls, affects class variables.
Static Method: Independent of class/instance.

Example:

class MyClass: class_var = 10 def instance_method(self): return self.class_var @classmethod def class_method(cls): return cls.class_var @staticmethod def static_method(): return "I don't use class variables" obj = MyClass() print(obj.instance_method()) # 10 print(MyClass.class_method()) # 10 print(MyClass.static_method()) # "I don't use class variables"

6. What is the difference between __str__() and __repr__()?

__str__() is for user-friendly output.
__repr__() is for debugging, should return a valid Python expression.

Example:

class Example: def __repr__(self): return "Example()" def __str__(self): return "This is an example" obj = Example() print(str(obj)) # This is an example print(repr(obj)) # Example()

7. How does Python’s __call__ method work?

It allows objects to be called like functions.

Example:

class CallableExample: def __call__(self, x): return x * 2 obj = CallableExample() print(obj(5)) # 10

8. What are Python descriptors?

Descriptors define how attributes are accessed.
They implement __get__, __set__, and __delete__.

Example:

class Descriptor: def __get__(self, instance, owner): return "Getting value" def __set__(self, instance, value): print(f"Setting value to {value}") class Example: attr = Descriptor() obj = Example() print(obj.attr) # "Getting value" obj.attr = 10 # "Setting value to 10"

9. How does Python implement method resolution order (MRO)?

Python uses C3 linearization (DFS + Breadth-First Search) for method resolution.

Example:

class A: pass class B(A): pass class C(A): pass class D(B, C): pass print(D.mro()) # [D, B, C, A, object]

10. What is monkey patching?

Modifying a class or module at runtime.

Example:

class Example: def greet(self): return "Hello" def new_greet(self): return "Hi!" Example.greet = new_greet print(Example().greet()) # "Hi!"

11. What is a Python closure?

A closure is a function that remembers variables from its enclosing scope.

Example:

def outer_function(x): def inner_function(y): return x + y return inner_function closure = outer_function(10) print(closure(5)) # 15

12. What are weak references in Python?

Weak references allow objects to be garbage collected.

Example:

import weakref class Example: pass obj = Example() weak = weakref.ref(obj) print(weak()) # <__main__.Example object> del obj print(weak()) # None (garbage collected)

13. What is the @property decorator?

@property allows defining getters and setters in a Pythonic way.

Example:

class Example: def __init__(self, value): self._value = value @property def value(self): return self._value @value.setter def value(self, new_value): self._value = new_value obj = Example(10) print(obj.value) # 10 obj.value = 20 print(obj.value) # 20

14. What is a metaclass and how is it used?

A metaclass controls class creation.

Example:

15. How does Python handle multiple inheritance conflicts?

Python resolves conflicts using C3 Linearization (MRO).

Example:

class A: def greet(self): return "A" class B(A): def greet(self): return "B" class C(A): def greet(self): return "C" class D(B, C): pass print(D().greet()) # "B" (MRO: D → B → C → A)

Python Fundamentals

Q1: What are Python’s key features?

Interpreted
Dynamically typed
Object-oriented
High-level and easy to read
Large standard library
Supports garbage collection

Data Structures in Python

Q2: What are the differences between a list and a tuple?

FeatureList (list)Tuple (tuple)

MutabilityMutable (can be modified)Immutable (cannot be modified)

PerformanceSlowerFaster

Syntaxlist = [1, 2, 3]tuple = (1, 2, 3)

Use CaseWhen frequent modifications are neededWhen data should not change

Example:

my_list = [1, 2, 3] my_list[0] = 10 # Allowed my_tuple = (1, 2, 3) # my_tuple[0] = 10 # TypeError: 'tuple' object does not support item assignment

Functions & Decorators

Q3: What are *args and kwargs in Python?

args allows a function to accept any number of positional arguments.
kwargs allows a function to accept any number of keyword arguments.

Example:

def example_function(*args, **kwargs): print("Positional:", args) print("Keyword:", kwargs) example_function(1, 2, 3, name="Alice", age=25) # Output: # Positional: (1, 2, 3) # Keyword: {'name': 'Alice', 'age': 25}

Object-Oriented Programming (OOP)

Q4: What is method overriding in Python?

Method overriding allows a child class to redefine a method from its parent class.

Example:

class Parent: def show(self): print("Parent method") class Child(Parent): def show(self): # Overriding the parent method print("Child method") obj = Child() obj.show() # Output: Child method

Memory Management

Q5: How does Python manage memory?

Uses reference counting and garbage collection.
Objects with zero references are automatically deleted.
Uses a generational garbage collector for efficiency.

Exception Handling

Q6: What is the difference between try-except and try-finally?

try-except handles exceptions.
try-finally ensures a block of code always runs, even if an exception occurs.

Example:

try: x = 1 / 0 except ZeroDivisionError: print("Cannot divide by zero") finally: print("This will always execute")

Multithreading & Concurrency

Q7: What is the Global Interpreter Lock (GIL)?

The GIL ensures that only one thread runs at a time.
It affects CPU-bound tasks but not I/O-bound tasks.

Example:

import threading def task(): for _ in range(1000000): pass t1 = threading.Thread(target=task) t2 = threading.Thread(target=task) t1.start() t2.start() t1.join() t2.join()

(Thread execution is not truly parallel due to GIL.)

File Handling

Q8: How do you read a file line by line?

Example:

with open("example.txt", "r") as file: for line in file: print(line.strip()) # Removes trailing newline

Database Handling

Q9: How do you connect Python to a database using SQLite?

Example using sqlite3:

import sqlite3 conn = sqlite3.connect("my_database.db") # Connect to database cursor = conn.cursor() cursor.execute("CREATE TABLE IF NOT EXISTS users (id INTEGER, name TEXT)") cursor.execute("INSERT INTO users (id, name) VALUES (?, ?)", (1, "Alice")) conn.commit() conn.close()

Web Development (Flask)

Q10: How do you create a simple Flask API?

Example:

from flask import Flask app = Flask(__name__) @app.route("/") def home(): return "Hello, Flask!" if __name__ == "__main__": app.run(debug=True)

Data Science & Pandas

Q11: How do you handle missing values in Pandas?

import pandas as pd df = pd.DataFrame({"A": [1, None, 3], "B": [4, 5, None]}) df.fillna(0, inplace=True) # Replaces NaN with 0 print(df)

Regular Expressions (Regex)

Q12: How do you validate an email using regex?

import re pattern = r"^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$" email = "test@example.com" if re.match(pattern, email): print("Valid Email") else: print("Invalid Email")

Python Performance Optimization

Q13: How can you optimize Python performance?

Use list comprehensions instead of loops.
Use generators to save memory.
Use built-in functions like sum(), max(), min().
Use NumPy for numerical computations.

Example:

# Using list comprehension (faster) squares = [x**2 for x in range(10)]

API Requests

Q14: How do you send an HTTP request using requests?

import requests response = requests.get("https://api.github.com") print(response.status_code) # 200 for success

Multithreading vs Multiprocessing

Q15: When should you use threading vs multiprocessing?

Use threading for I/O-bound tasks (e.g., web scraping, file I/O).
Use multiprocessing for CPU-bound tasks (e.g., large computations).

Example:

from multiprocessing import Pool def square(n): return n * n with Pool(4) as p: print(p.map(square, [1, 2, 3, 4])) # [1, 4, 9, 16]

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Python Interview Questions and Answers

Top 100 Python Interview Questions for Freshers

1. What is Python?

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

2. What are Python's key features?

Easy to learn and use

Interpreted language

Dynamically typed

Extensive standard library

Open-source and community-supported

Supports multiple paradigms

Platform-independent​

3. What is PEP 8?

PEP 8 is Python’s style guide that provides best practices for writing clean, readable, and consistent code.

4. What is the difference between a list and a tuple?

List: Mutable (can be changed), uses []

Tuple: Immutable (cannot be changed), uses ()​​

5. What is the difference between Python 2 and Python 3?

Python 3 supports Unicode by default, uses print() as a function, and has improved syntax and standard library.

6. How is memory managed in Python?

Python uses automatic memory management, including garbage collection, reference counting, and a private heap.

7. What are Python’s data types?

Numeric types: int, float, complex

Sequence types: list, tuple, range

Text type: str

Set types: set, frozenset

Mapping type: dict

Boolean type: bool

Binary types: bytes, bytearray, memoryview

8. What are Python's built-in data structures?

List, Tuple, Dictionary, Set

9. What is the difference between is and ==?

is checks object identity (same memory location).

== checks value equality.

10. What are Python functions?

Functions are reusable blocks of code that perform specific tasks. Defined using def.

11. What is the difference between deepcopy() and copy()?

copy.copy() creates a shallow copy (references nested objects).

copy.deepcopy() creates a deep copy (completely independent clone).

12. What is a lambda function?

A small anonymous function defined using lambda keyword.

add = lambda x, y: x + y print(add(3, 4)) # Output: 7

13. What are Python decorators?

Functions that modify the behavior of other functions without modifying their code.

def decorator(func): def wrapper(): print("Before function call") func() print("After function call") return wrapper @decorator def say_hello(): print("Hello") say_hello()

14. What are *args and kwargs in Python?

args: Allows passing a variable number of positional arguments.

kwargs: Allows passing a variable number of keyword arguments.

def example(*args, **kwargs): print(args, kwargs) example(1, 2, 3, name="Alice", age=25)

15. What is the difference between a module and a package?

Module: A .py file containing Python code.

Package: A collection of modules, containing an __init__.py file.​

16. What is the difference between @staticmethod, @classmethod, and instance methods?

Instance method: Works with instance (self).

Class method: Uses @classmethod, takes cls as the first parameter.

Static method: Uses @staticmethod, doesn’t take self or cls​

17. How does exception handling work in Python? try: x = 1 / 0 except ZeroDivisionError as e: print(f"Error: {e}") finally: print("Execution completed")

18. What are Python’s file handling modes?

"r" – Read

"w" – Write (overwrite)

"a" – Append

"rb"/"wb" – Binary read/write​

19. What is list comprehension? numbers = [x**2 for x in range(10) if x % 2 == 0] print(numbers) # [0, 4, 16, 36, 64]

20. How do you implement multithreading in Python? import threading def print_numbers(): for i in range(5): print(i) thread = threading.Thread(target=print_numbers) thread.start() ​

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

Platform-independent

Tuple: Immutable (cannot be changed), uses ()

Package: A collection of modules, containing an init.py file.

Static method: Uses @staticmethod, doesn’t take self or cls

17. How does exception handling work in Python?
try: x = 1 / 0 except ZeroDivisionError as e: print(f"Error: {e}") finally: print("Execution completed")

"rb"/"wb" – Binary read/write

19. What is list comprehension?
numbers = [x**2 for x in range(10) if x % 2 == 0] print(numbers) # [0, 4, 16, 36, 64]

20. How do you implement multithreading in Python?
import threading def print_numbers(): for i in range(5): print(i) thread = threading.Thread(target=print_numbers) thread.start()