Python Basics

1. What are Python's key features?

• Easy to learn and read.
• Interpreted and dynamically typed.
• Supports multiple programming paradigms (OOP, functional, procedural).
• Has a large standard library.
• Extensible and embeddable.

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

• Python 2 is outdated and no longer maintained.
• Python 3 uses print() as a function (print "Hello" → print("Hello")).
• Unicode handling is better in Python 3 (str is Unicode by default).
• Division behavior changed (5/2 → 2.5 instead of 2).

3. How does Python handle memory management?

• Uses Garbage Collection (GC) to reclaim unused memory.
• Uses Reference Counting to track objects.
• Uses a private heap for storing objects.

4. What is PEP 8, and why is it important?

• PEP 8 is the Python style guide that helps make code readable and consistent.
• It covers naming conventions, indentation, whitespace, and more.

5. Explain Python's data types.

• int: Whole numbers (e.g., 10, -5, 1000).
• float: Decimal numbers (e.g., 3.14, -2.5).
• list: Ordered, mutable collection (e.g., [1, 2, 3]).
• tuple: Ordered, immutable collection (e.g., (1, 2, 3)).
• dict: Key-value pairs (e.g., {"name": "Alice", "age": 25}).
• set: Unordered collection of unique items (e.g., {1, 2, 3}).

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

• List is mutable ([1, 2, 3] → list[0] = 10).
• Tuple is immutable ((1, 2, 3) → Cannot modify elements).
• Tuples are faster than lists for fixed data.

7. How do you handle exceptions in Python? Give an example.

Use try-except to catch errors.

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

8. Explain the use of the with statement in Python.

Used for resource management (e.g., file handling).

with open("file.txt", "r") as file:
    content = file.read()  # File automatically closes after this block.

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

• is: Checks if two variables point to the same object in memory.
• ==: Checks if values are equal.

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

10. How does Python handle mutability?

• Mutable objects: Can be changed (list, dict, set).
• Immutable objects: Cannot be changed (int, float, tuple, string).

11. Explain the difference between deepcopy() and copy().

• copy.copy() : Creates a shallow copy (nested objects remain shared).
• copy.deepcopy() : Creates a deep copy (fully independent copy).

import copy
a = [[1, 2], [3, 4]]
b = copy.copy(a)  # Shallow copy
c = copy.deepcopy(a)  # Deep copy

12. What is the difference between append() and extend() in lists?

• append(): Adds a single element.
• extend(): Adds multiple elements from an iterable.

lst = [1, 2, 3]
lst.append([4, 5])  # [1, 2, 3, [4, 5]]
lst.extend([4, 5])  # [1, 2, 3, 4, 5]

13. How do you remove duplicates from a list?

lst = [1, 2, 2, 3, 4, 4, 5]
unique_lst = list(set(lst))  # {1, 2, 3, 4, 5}

14. What are *args and **kwargs in Python functions?

• *args: Passes multiple positional arguments.
• **kwargs: Passes multiple keyword arguments.

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

example(1, 2, 3, name="Alice", age=25)  
# Output: (1, 2, 3) {'name': 'Alice', 'age': 25}

15. Explain the difference between a shallow copy and a deep copy.

• Shallow Copy: Copies references (changes affect both copies).
• Deep Copy: Creates a completely independent copy.

16. How do you swap two variables in Python without using a temporary variable?

a, b = 10, 20
a, b = b, a
print(a, b)  # 20, 10

17. What is the difference between global, nonlocal, and local variables?

• local: Defined inside a function.
• global: Declared outside functions, accessible everywhere.
• nonlocal: Used inside nested functions to modify variables from the outer function.

18. Explain list comprehension with an example.

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

19. How do you reverse a string in Python?

text = "Python"
print(text[::-1])  # "nohtyP"

20. How do you read and write files in Python?

# Writing to a file
with open("example.txt", "w") as f:
    f.write("Hello, Python!")

# Reading from a file
with open("example.txt", "r") as f:
    content = f.read()
print(content)  # "Hello, Python!"