Python Interview Questions

This document provides a curated list of Python interview questions commonly asked in technical interviews for Data Scientists, Backend Engineers, and Python Developers. It covers core concepts, internals, concurrency, and advanced language features.

This is updated frequently but right now this is the most exhaustive list of type of questions being asked.

Code Examples

1. Decorator for Timing Functions

import time
import functools

def timer_decorator(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        start_time = time.perf_counter()
        result = func(*args, **kwargs)
        end_time = time.perf_counter()
        run_time = end_time - start_time
        print(f"Finished {func.__name__!r} in {run_time:.4f} secs")
        return result
    return wrapper

@timer_decorator
def complex_calculation(n):
    return sum(i**2 for i in range(n))

complex_calculation(1000000)

2. Context Manager for Files

class FileManager:
    def __init__(self, filename, mode):
        self.filename = filename
        self.mode = mode
        self.file = None

    def __enter__(self):
        self.file = open(self.filename, self.mode)
        return self.file

    def __exit__(self, exc_type, exc_value, exc_traceback):
        if self.file:
            self.file.close()

# Usage
# with FileManager('test.txt', 'w') as f:
#     f.write('Hello, World!')

3. Asynchronous Pattern

import asyncio

async def fetch_data(delay, id):
    print(f"Fetching data {id}...")
    await asyncio.sleep(delay)  # Simulate I/O op
    print(f"Data {id} fetched")
    return {"id": id, "data": "sample"}

async def main():
    # Run tasks concurrently
    tasks = [fetch_data(1, 1), fetch_data(2, 2), fetch_data(1.5, 3)]
    results = await asyncio.gather(*tasks)
    print(results)

# asyncio.run(main())

Questions asked in Google interview

• Explain the Global Interpreter Lock (GIL) and its impact on multi-threading.
• How does Python's garbage collection mechanism work? (Reference counting vs Generational GC).
• Write a custom decorator that caches function results (Memoization).
• How would you debug a memory leak in a long-running Python process?
• Explain the method resolution order (MRO) works with multiple inheritance.
• Write code to implement a thread-safe singleton.
• How to optimize a CPU-bound Python script?
• Explain the key differences between Python 2 and Python 3.
• How to implement a context manager using contextlib.
• Write code to parse a large log file without loading it entirely into memory.

Questions asked in Meta interview

• How are dictionaries implemented in Python? (Hash collision handling).
• Explain the difference between __new__ and __init__.
• Write code to flatten a deeply nested dictionary.
• How does asyncio differ from threading? When to use which?
• Explain the concept of metaclasses and a use case.
• Write a generator that yields Fibonacci numbers indefinitely.
• How to handle circular imports in a large project?
• Explain the descriptor protocol and how properties work.
• How would you implement a custom iterator?
• Write code to validate and parse JSON data using dataclasses or pydantic.

Questions asked in Amazon interview

• Write code to reverse a string without using built-in methods.
• Explain the difference between deep copy and shallow copy.
• How to handle exceptions in a large-scale application?
• Write code to find the most frequent element in a list efficiently.
• Explain the use of *args and **kwargs.
• How to implement a producer-consumer problem using queue?
• Explain the difference between @staticmethod, @classmethod, and instance methods.
• Write code to sort a list of dictionaries by a specific key.
• How does variable scope work in Python (LEGB rule)?
• Explain what if __name__ == "__main__": does.

Questions asked in Netflix interview

• How to optimize Python for high-throughput network applications?
• Explain the internals of CPython execution loop.
• Write code to implement a rate limiter using Redis and Python.
• How to handle dependency management in a microservices architecture?
• Explain how gunicorn or uwsgi works with Python web apps.
• Write code to implement async HTTP requests using aiohttp.
• How to profile Python code to find bottlenecks? (cProfile, py-spy).
• Explain the challenge of serialization (pickling) in distributed systems.
• How to implement rigorous unit testing with pytest?
• Write code to process a stream of data using generators.

Additional Resources

• Official Python Documentation
• Real Python Tutorials
• Fluent Python (Book)
• Python Internals (GitHub)
• Hitchhiker's Guide to Python