Python Interview Cheatsheet

This page is a curated, question-indexed map into the rest of the cheatsheet. Each entry is a question you are likely to see in a Python interview, followed by a link that jumps directly to the section of the notes that answers it. It is intentionally a navigation layer — the actual explanations, code, and caveats live in the linked sections.

Use it two ways:

• Drilling a topic: pick a group (e.g. Asyncio) and walk every question.
• Quick review before an interview: read the questions, and for any you cannot confidently answer in one or two sentences, click through.

Python Language Fundamentals

• What does from __future__ import ... do, and which future imports still matter? Print Function · Division · Annotations
• What is Ellipsis (...) used for in modern Python? Ellipsis
• How do for/while ... else clauses work? for ... else ... · while ... else ...
• What does try ... except ... else do that a plain try ... except does not? try ... except ... else ...
• How does Python handle Unicode vs bytes, and what is a code point? Characters · Unicode Code Point

Data Structures & Collections

• What is the difference between a shallow copy and a deep copy of a list? Copy Lists
• Why can [[]] * n surprise you? Initialize Lists with Multiplication Operator
• What is a list comprehension, and when is a generator expression better? List Comprehensions
• How do you get (index, value) pairs while iterating? enumerate()
• How is a dict iterated, and what does dict.items() / dict.keys() return? dict.keys() · dict.items()
• dict.setdefault vs collections.defaultdict — which fits which use case? setdefault and defaultdict
• How do you merge two dicts (pre-3.9 and post-3.9)? Merge Two Dictionaries in Python
• How would you implement an LRU cache from scratch? Implement LRU Cache with OrderedDict
• How do you dedupe a list while preserving order? Remove Duplicates from a List
• When would you use heapq instead of sorting? Basic Heap Operations · Priority Queue
• How do you emulate a dict-like object with dunder methods? Emulate a Dictionary with Special Methods

Functions & Decorators

• What do *args and **kwargs really do, and how do you forward them? Variable Arguments · Unpack Arguments
• What is the difference between keyword-only and positional-only arguments? Keyword-Only Arguments · Positional-Only Arguments
• What is a closure, and what does it capture? Closure
• How do decorators work, and how do you write one that takes arguments? Decorator · Decorator with Arguments
• functools.lru_cache vs functools.partial — what do they do? lru_cache · Partial Functions
• How does functools.singledispatch implement function overloading? singledispatch

Iterators & Generators

• Generator function vs generator expression — when is each idiomatic? Generator Function vs Generator Expression
• How do you send a value into a running generator? Send Values to Generator
• What does yield from do, and how does it compose generators? yield from Expression · yield from with Return
• How do you build an iterable class with a generator method? Iterable Class via Generator
• How do you implement a context manager as a generator with @contextmanager? Context Manager via Generator · What @contextmanager does
• What is an async generator, and how does it differ from a normal generator? Async Generator

Classes & OOP

• __new__ vs __init__ — when does each run? new vs init
• __str__ vs __repr__ — who calls which? str and repr
• How does the descriptor protocol work? Descriptor Protocol
• What is the context manager protocol (__enter__ / __exit__)? Context Manager Protocol
• @staticmethod vs @classmethod — when to use which? staticmethod and classmethod
• What is MRO, and how does C3 linearization resolve the diamond problem? The Diamond Problem (MRO)
• When should you define __slots__? slots
• How do you define a class at runtime with type(...)? Declare Class with type()
• What are abstract base classes, and how does abc enforce them? Abstract Base Classes
• How do you implement a callable object? Callable with call
• What does @property buy you over plain getters/setters? @property Decorator

Concurrency

• What is the GIL, and how does it affect CPU-bound vs I/O-bound code? Understanding the GIL
• Threading vs multiprocessing — when would you reach for each? Creating Threads · Creating Processes
• Lock vs RLock — what is the difference? Lock · RLock
• How do you synchronize with Event, Condition, or Barrier? Event · Condition · Barrier
• How would you build a producer-consumer pipeline with queue.Queue? Producer-Consumer with Queue
• What is a deadlock, and how do you prevent one? Deadlock Example and Prevention
• How do you share state across processes (Queue, Pipe, Value, Manager)? Sharing Data with Queue · Shared Memory · Manager
• ThreadPoolExecutor vs ProcessPoolExecutor — how do you pick? ThreadPoolExecutor · ProcessPoolExecutor
• How do you process results from many futures as they complete? as_completed

Asyncio

• What actually happens when you call asyncio.run(coro())? asyncio.run
• asyncio.create_task vs awaiting a coroutine directly — what is the difference? Tasks
• How do asyncio.gather and asyncio.wait differ? gather · wait for first completed
• How do you time-bound an awaitable? Waiting with Timeout
• What is an async context manager, and how do you write one? Async Context Managers · @asynccontextmanager
• How do you call blocking code from an async function without blocking the loop? Running Blocking Code in Executor
• How do you handle exceptions raised inside tasks? Exception Handling in Tasks
• How do you rate-limit concurrency in asyncio? Semaphores
• What is a graceful shutdown in asyncio? Graceful Shutdown
• Conceptually, what is a coroutine and how does the event loop drive it? What is a Coroutine? · Event Loop

Common Gotchas

• Why is using a mutable default argument (def f(x=[])) dangerous? Default Arguments

C Extensions & Interop

• How do you write a C extension module with the CPython C API? Simple C Extension · Parse Arguments
• How and why do you release the GIL in a C extension? Release the GIL
• How do you call into a shared library with ctypes? Loading Shared Libraries · Basic Type Mapping

Networking

• How do you resolve a hostname to an IP in Python? Address Info (DNS Resolution)
• Network byte order — when and why do you need htons / ntohs? Network Byte Order Conversion
• How do you build a minimal TLS echo server and client? Simple TLS Echo Server · TLS Client
• What is mutual TLS (mTLS), and why would a service require it? Mutual TLS (mTLS)

Databases

• What does a SQLAlchemy engine actually hold, and how do connections work? Create an Engine · Database URL Format
• How do you run raw SQL safely with parameters? Connect and Execute Raw SQL
• Transactions in SQLAlchemy — who commits, and when? Transaction Management
• Core vs ORM — what does the ORM add on top? Declarative Base · Session Basics

Security & Crypto

• What are the common cryptographic mistakes to avoid? Common Mistakes · Security Checklist
• Why should you prefer secrets over random for tokens? Secure Random Generation · Weak Random
• What is a timing attack, and how do you defend against one? Timing Attacks
• How does SQL injection happen in Python, and how is it prevented? SQL Injection

See Also

If a question above is not covered, the top-level indices are the best next stop:

• Basic — Python core language and data structures
• Concurrency — Threading, multiprocessing, futures
• Asyncio — Asyncio and async patterns
• Network — Sockets and SSL/TLS
• Database — SQLAlchemy core and ORM
• Security — Cryptography and common vulnerabilities
• Extension — C extensions and FFI