Question 1

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

Accepted Answer

Lists are mutable (can be changed after creation); tuples are immutable (fixed after creation). Tuples use less memory and are slightly faster, suitable for fixed data and dictionary keys.

Question 2

What is a Python decorator? Write one from scratch.

Accepted Answer

A decorator is a function that takes another function as input and returns a modified version of it — without changing the original source code. The @syntax is syntactic sugar for func = decorator(func).

Question 3

What is the Python GIL? How does it affect concurrency?

Accepted Answer

The Global Interpreter Lock (GIL) is a mutex in CPython that allows only one thread to execute Python bytecode at a time. It makes CPU-bound threading ineffective but doesn't affect I/O-bound threads or multiprocessing.