Python Interview Questions

1. What are Python's key features?

• Easy to learn and use: Python has a simple, readable syntax.
• Interpreted Language: Python code is executed line by line.
• Dynamically Typed: No need to declare data types; Python detects them automatically.
• Object-Oriented: Supports classes, inheritance, and encapsulation.
• Extensive Libraries: Includes modules for math, OS, web, databases, machine learning, etc.
• Portable: Code written in one OS can run on another.
• Open Source: Freely available and supported by a strong community.

2. What is the difference between a list and a tuple in Python?

3. How is memory managed in Python?

• Python uses a private heap to store objects and data structures.
• Automatic garbage collection reclaims memory from unused objects.
• Reference counting and the cyclic garbage collector manage memory.
• Developers can use the gc module to interact with the collector.

4. What are Python's data types?

• Numeric: int, float, complex
• Sequence: list, tuple, range
• Text: str
• Set: set, frozenset
• Mapping: dict
• Boolean: bool
• Binary: bytes, bytearray, memoryview
• NoneType: None

5. What is PEP 8 and why is it important?

• PEP 8 is the official style guide for Python code.
• Promotes readability and consistency across the Python community.
• Covers naming conventions, indentation (4 spaces), line length, imports, etc.
• Following PEP 8 ensures maintainable and professional code.

6. What is the difference between is and == in Python?

== checks value equality (do the objects have the same data?).

is checks identity equality (are both variables pointing to the same object in memory?).

a = [1, 2]
b = [1, 2]
print(a == b)  # True
print(a is b)  # False

7. What are Python's mutable and immutable data types?

• Mutable (can be changed): list, dict, set, bytearray
• Immutable (cannot be changed): int, float, str, tuple, frozenset, bytes

8. What are *args and **kwargs?

• *args: Allows passing a variable number of non-keyword arguments to a function.
• **kwargs: Allows passing a variable number of keyword arguments.

def example(*args, **kwargs):
    print(args)      # tuple
    print(kwargs)    # dictionary

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

10. How does Python handle type conversion?

• Implicit Conversion: Automatically done by Python (e.g., int to float).
• Explicit Conversion: Done manually using functions like int(), float(), str(), etc.

a = 5
b = 2.0
c = a + b  # Implicitly converted to float

Intermediate Level

11. What are Python decorators and how are they used?

A decorator is a function that adds functionality to another function without modifying its code.

Typically used for logging, access control, memoization, etc.

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

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

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

• Shallow Copy: Copies outer object, not nested objects. (copy.copy())
• Deep Copy: Copies everything recursively. (copy.deepcopy())

import copy
a = [[1, 2], [3, 4]]
b = copy.copy(a)      # changes in inner lists affect both
c = copy.deepcopy(a)  # fully independent copy

13. What is a Python generator? How is it different from an iterator?

• Generators use yield to produce a sequence of results lazily.
• Generators are a type of iterator but are more memory efficient.

def gen():
    yield 1
    yield 2

Generators do not store all values in memory; they generate one value at a time.

14. Explain the Global Interpreter Lock (GIL).

• GIL is a mutex that allows only one thread to execute at a time in the CPython interpreter.
• It makes multi-threading limited for CPU-bound tasks but is fine for I/O-bound operations.
• Alternative: use multiprocessing instead of threads for CPU-heavy tasks.

15. What are Python's lambda functions?

• A lambda function is a small anonymous function defined using the lambda keyword.
• Syntax: lambda arguments: expression

add = lambda x, y: x + y
print(add(2, 3))  # Output: 5

16. How does Python handle exception handling? Give examples.

• Uses try, except, finally, and else blocks.
• Catches and handles errors gracefully.

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Can't divide by zero")
finally:
    print("Cleanup")

17. What are list comprehensions and how do they work?

A concise way to create lists.

squares = [x**2 for x in range(5)]
# Output: [0, 1, 4, 9, 16]

Supports conditions: [x for x in range(10) if x % 2 == 0]

18. Explain Python's with statement and context managers.

• Used for resource management (like files), ensuring cleanup.
• A context manager implements __enter__ and __exit__.

with open('file.txt') as f:
    data = f.read()
# File is automatically closed

19. What is the purpose of __init__.py file?

• Marks a directory as a Python package.
• Can also include initialization code for the package.
• Required in Python 2, optional in Python 3 for basic package creation.

20. What are Python modules and packages? How do you import them?

• Module: A .py file containing Python code (functions, classes).
• Package: A folder containing modules and an optional __init__.py.

Importing:

import math
from datetime import datetime
import mypackage.mymodule