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SOLID Principles in Python 4 Understanding Big O Notation in Python 4 Programming Paradigms in Python 3 DRY and KISS Principles in Python 3 Creational Design Patterns (GoF) 7 Structural Design Patterns (GoF) 7 Behavioral Design Patterns (GoF) 9

Is Python interpreted or compiled? 5 Mutable vs Immutable Types in Python 9 Variable Scope in Python 3 Introspection in Python 3 What is the difference between is and ==? 3 Difference Between __init__() and __new__() in Python 3 Types of Imports in Python 3 Class, Iterator, and Generator in Python 3 Metaclass and Loop Variable in Python 3 Difference Between Iterators and Generators 3 Difference Between staticmethod and classmethod in Python 3 Decorators and Context Managers in Python 3 args and *kwargs in Python 3 Testing in Python 5 Fixtures and Patch in pytest 3 Lambda Functions and Their Usage with map, filter, and reduce in Python 3 Shallow vs deep copy Hashable Objects in Python 3 Argument Passing in Python: By Reference or By Value? 3 Python, Backend, and Architecture Learning Notes 4 Python, Backend, and Architecture Learning Notes 3 Generators and Iterators in Python 3 __eq__ vs __hash__ Enum vs StrEnum 6 Debugging and introspecting async code 5 Application debugging and introspection 5 Python memory model — allocation, refcounting, GC __slots__ — when it saves memory and what it breaks weakref — References That Don't Prevent GC 8 String interning and the small-int cache dis — inspecting Python bytecode dict internals list internals match/case — structural pattern matching (3.10+) What's new in Python 3.12-3.14 5 Python Packaging — pip, Poetry, uv 5 Virtual Environments and Lockfiles 6 pyproject.toml and Building Packages 6 Dependency Resolution and Supply-Chain Security 6 Profiling Python — cProfile, pstats, timeit Memory profiling — tracemalloc, memory_profiler, objgraph Why Python is slow — and how to mitigate it Native extensions — Cython, Numba, ctypes, PyO3 Async optimization — getting the most out of asyncio Debugging a Live Production Incident 5 collections — specialized containers itertools — efficient iterator combinators functools — higher-order function utilities contextlib — context manager helpers dataclasses — boilerplate-free data classes pathlib and logging 5 concurrent.futures — thread/process pools with a unified API dataclasses vs Pydantic v2 vs attrs 7 Mutable default arguments Late-binding closures is vs == and string/int interning bool is a subclass of int Class variable vs instance variable List multiplication and aliasing Chained comparisons Generator exhaustion async def returns a coroutine, doesn't run super() and MRO with multiple inheritance Walrus operator (:=) gotchas Comprehension scope += on an immutable inside a dict id() reuse after garbage collection Implicit string concatenation dict.get(k, default) and falsy values Floats and equality Dataclass mutable defaults Starred unpacking Exception swallowing in finally Circular imports Descriptor invocation order Empty class as a dict key 4 Metaclass vs class decorator pickle security nonlocal vs global yield from semantics Blocking calls in async def Decorator with arguments functools.wraps Collection complexity (list / tuple / set / dict) Truthiness of containers and falsy values Positional-only and keyword-only parameters (/ and *) Mutating a dict key after insertion True, 1, and 1.0 as the same dict key float('nan') as a dict key Self-referential dicts (and lists) Mutating a dict during iteration setdefault always evaluates the default __missing__ — and why .get() doesn't trigger it Merging dicts: {a, b} vs a | b vs update vs ChainMap Duplicate keys in dict comprehensions Inverting a dict — what could go wrong dict.fromkeys shares a single default object frozenset vs tuple as a dict key Dict insertion order — when did it become a guarantee? d[k] vs d.get(k) vs d.setdefault(k, v) vs defaultdict Dict shallow copy trap — nested mutables are shared Type hint basics: Optional, Union, Callable TypeVar and generics Protocol and structural typing TypedDict, Literal, Final, ClassVar Annotated and TypeGuard ParamSpec and Concatenate — typing decorators mypy vs pyright; strictness modes; runtime enforcement

Magic Methods and Attributes in Python 4 Classes in Python 4 Objects in Python 4 Polymorphism in Python 4 Encapsulation in Python 4 Inheritance in Python 4 Data Abstraction in Python 4 Descriptors 6 Python Protocols and Interfaces: A Comprehensive Guide 4 Metaclasses — Production Patterns 6

The GIL, and free-threaded Python 6 Concurrency vs. Parallelism in Python Async Programming 3 Difference Between Threads and Processes 4 Context Switching in Python Async Programming 4 Asynchronous Python and Coroutines 4 Event Loop Internals 9 Asyncio vs Threads in Python: A Comprehensive Comparison 4 Python Concurrency Models: Processes, Threads, and Asyncio 4 When to use processes 5 Synchronization Primitives in Python Comparing asyncio.Queue and threading.Queue in Python 4 TaskGroup and Structured Concurrency 5 Cancellation, timeouts and error handling in asyncio 7 run_in_executor and asyncio.to_thread 6 Concurrent.futures in Python: A Comprehensive Guide 4 ProcessPoolExecutor in Python: A Comprehensive Guide 4 anyio and Trio — structured concurrency 5 Async and concurrency

Integration tests 5 Mocking external APIs 5 Fixtures, parametrize and scope 5 Fixtures deep dive Parametrize patterns Mock, MagicMock, patch pytest-asyncio Hypothesis and property-based testing Coverage and branches Test doubles taxonomy Pytest Testing Framework QA methodology and test design 6 Test automation frameworks and API testing 6 QA engineering Test Strategy and the Test Pyramid 6 Integration and Contract Testing 6 Load and Performance Testing 7 Test Data, Flaky Tests, and CI Parallelization 6

WSGI vs ASGI — Common Interview Questions and Answers 3 aiohttp — ClientSession Lifecycle and Connection Pooling 6 aiohttp — Timeouts, Retries, and Pooling Patterns 6 aiohttp — Streaming and Server Framework 6 aiohttp vs httpx 6 Django F Object 7 Django Q Object 8 Django Bulk Operations Guide 3 Django Proxy Models Guide 3 Django Serializers and Actions Guide 3 Django Models vs QuerySets: Understanding the Difference 3 Django middleware 5 Django signals 5 CharField vs TextField in Django 3 settings.py 6 select_related vs prefetch_related in Django ORM 3 Django vs Django REST Framework (DRF) Guide 3 Async Django, Channels, and Async ORM 6 Django ORM: A Comprehensive Guide 3 Django Migrations: A Comprehensive Guide 4 Django ORM Relationships: One-to-Many, Many-to-Many, One-to-One 3 Django REST Framework (DRF) 4 DRF Serializers 5 DRF Validation 5 DRF Views: APIView, GenericAPIView, ViewSet 5 DRF Routers and Custom Actions 5 DRF Permissions 6 DRF Authentication 5 DRF Throttling 5 DRF Pagination 5 DRF Filtering, Searching, Ordering 5 DRF Nested Writable Serializers 5 DRF Performance and the N+1 Problem 6 Testing DRF APIs 5 DRF Exception Handling 5 DRF Versioning 5 DRF Schema and OpenAPI 5 Django FastAPI 5 FastAPI Basics and Setup - Interview Questions 4 Pydantic models in FastAPI 6 Dependencies and injection 7 Async and performance 6 Security and authentication 6 Testing a FastAPI app 6 Middleware 5 FastAPI project structure 5 FastAPI — Common Interview Questions and Answers 4 FastAPI and the event loop 5 Outbound auth, logging and caching 5 Exception handling 5 Writing a client for an external API 7 FastAPI: sync code in an async route, run_in_threadpool 6 BackgroundTasks vs Celery — Decision Matrix 6 response_model — Advanced Patterns 6 OpenAPI and the generated docs 6 Deployment 6 Flask 5 Litestar 4 Pydantic — Common Interview Questions and Answers 3 Pydantic in practice 5 Validation modes: before, after, strict, lax 5 Streamlit Overview - Interview Questions 3 Streamlit Basics and Widgets - Interview Questions 3 Streamlit Session State - Interview Questions 3 Streamlit Caching - Interview Questions 3 Streamlit Multipage Apps - Interview Questions 3 Streamlit LLM Chat Apps - Interview Questions 3 Streamlit Deployment and Secrets - Interview Questions 3 Streamlit Testing and Advanced Topics - Interview Questions 3

Idempotency 5 JWT Authentication: What, When, and How 3 Status codes 5 PUT vs PATCH: Understanding the Difference 3 REST principles REST Versioning and Pagination 6 Richardson Maturity Model and HATEOAS 6 REST Error Handling and HTTP Caching 7 Stateful vs Stateless (REST and beyond) 7

SQL and NoSQL 6 NoSQL Decision Guide — Which Store, and When 6 Apache Cassandra 7 Elasticsearch — Inverted Index Fundamentals 6 Elasticsearch — Query DSL and BM25 Scoring 7 Elasticsearch — Mappings, Field Types, and Schema Evolution 7 Elasticsearch — Aggregations 7 Elasticsearch — Vector Search and kNN 7 Elasticsearch — Python Client and Production Pitfalls 7 OpenSearch and the fork 5 MongoDB — Overview 6 MongoDB — Indexes 6 MongoDB — Aggregation Pipeline 7 MongoDB — Transactions, Read & Write Concerns 6 MongoDB — Replica Sets and Sharding 7 MongoDB — Pitfalls and Performance 7 NoSQL Databases SQL fundamentals Database Indexes — Fundamentals 10 How a query is processed 6 SQL Transactions 4 Relationships and Keys in PostgreSQL 4 SQLAlchemy 3 N+1 query problem Transactions and isolation levels Connection pooling EXPLAIN and EXPLAIN ANALYZE Index types Window functions and CTEs Zero-downtime migrations Sharding and Partitioning 10 CAP, ACID, BASE, PACELC 6 Alembic 6 MySQL 5 SQLite 5 VACUUM, autovacuum, table bloat, and transaction wraparound 7 PostgreSQL Advisory Locks 6 Replication and Logical Decoding 6 WAL, Checkpoints, and fsync 6 Isolation Anomalies Across Databases — Postgres vs MySQL vs SQLite 7 Core vs ORM 5 Engine, Connection, Session 6 Declarative Models 6 Relationships 6 Querying — 2.0 select() style 6 Loading Strategies and N+1 6 Unit of Work and Identity Map 7 Session Lifecycle 6 Transactions, Savepoints, Isolation 6 Connection Pooling 6 Async SQLAlchemy 6 Bulk Operations and Performance 6 Testing Patterns 6 Common Pitfalls 7 SQLAlchemy — Deep Topical Notes

What is Redis 7 Cache Stampede and Mitigation Patterns 6 Redlock and the Kleppmann Critique 6 Persistence, eviction and memory 7 Replication, Sentinel and Cluster 6 Pub/sub and Streams 6 Redis from Python 6 Redis Valkey 5

Kafka vs RabbitMQ — choosing a message broker What is Celery 7 How to Make Retry in Celery 4 Celery — Common Interview Questions and Answers 4 Celery Task Idempotency 6 Dead-Letter Queue (DLQ) for Celery 6 Celery Canvas: Chord, Group, Chain — and Their Pitfalls 6 Celery Beat: HA, Scheduling, and Lock Contention 6 Celery IBM MQ — Overview for Python Backends 7 What is Kafka 7 Kafka: Log Compaction, Rebalancing, and Advanced Topics 7 Kafka — Schema Registry and Python Client Comparison 7 Kafka delivery semantics — at-most-once, at-least-once, exactly-once Producer configuration and durability 6 Apache Kafka NATS and JetStream 5 What is RabbitMQ 5 RabbitMQ exchanges and routing RabbitMQ Exchanges, Queues, DLX, and Quorum Queues 7 RabbitMQ — Common Interview Questions and Answers 4 RabbitMQ RQ (Redis Queue) 5 Stream Processing — Windowing, Watermarks, State 7 What is Temporal? 3 Workflows vs Activities 4 Temporal vs Celery vs Other Orchestrators 4 Temporal — Common Interview Questions and Answers 4

Authentication overview 6 SSO 6 Amazon Cognito for Python Backends 7 JWT Basics — Structure and Encoding 6 JWT Signing Algorithms 7 JWT Claims 7 Access and Refresh Tokens 8 JWT Revocation and Logout 7 Python JWT with PyJWT 7 JWT vs Session-Based Auth 7 The JOSE Family — JWS, JWE, JWK, JWA, JWT 7 JWT and the JOSE Family SAML 2.0 Deep Dive 6 OIDC and OAuth 2.0 Flows 7 Tokens: ID, Access, Refresh 7 Session Management with SSO 7 Single Logout (SLO) 6 SCIM and User Provisioning 6 Group, Role, and Claim Mapping 6 SSO Attack Vectors 7 MFA and Step-Up Authentication 6 Multi-Tenant SSO 6 Python Libraries for SSO 6 SSO Common Pitfalls 6 SSO — Deep Topical Notes

API Protocols Comparison — REST, GraphQL, gRPC, SOAP 6 GraphQL Overview 5 GraphQL Schema and Types 6 Queries, Mutations, Subscriptions 6 Resolvers, N+1, and DataLoader 6 GraphQL Pagination — Relay Connections 6 GraphQL Errors and Versioning 6 GraphQL Security 6 Python GraphQL Libraries 6 gRPC Overview 5 Protocol Buffers (Protobuf) 6 gRPC Service Types — Unary and Streaming 7 gRPC's HTTP/2 Basis 6 Python gRPC 6 gRPC Interceptors, Metadata, and Auth 6 gRPC Error Handling 6 gRPC Load Balancing and gRPC-Web 6 HTTP HTTP Versions — 1.0, 1.1, 2, 3 6 HTTP Semantics and Caching 7 How to Configure Communication Between Multiple VMs via Nginx 3 Nginx Architecture 6 Nginx Directives and Contexts 6 Nginx Location Matching 6 proxy_pass and the Trailing Slash Trap 6 Nginx Upstreams and Load Balancing 6 Nginx + Gunicorn — The Canonical Python Deploy 6 Nginx Caching 6 Nginx Static Files and Compression 6 Nginx WebSocket Proxying 6 Nginx Rate Limiting 6 Nginx TLS Configuration 6 Nginx Troubleshooting 6 Nginx vs Alternatives 6 SOAP Overview 6 SOAP Envelope and WSDL 6 WS-Security 6 Python SOAP Libraries 6 When You'll See SOAP 6 SOAP Server-Sent Events (SSE) 7 WebSocket Protocol 7 Python WebSocket Implementations 6 WebSocket vs Alternatives 7 WebSocket Authentication 7 WebSocket Connection Management 7 WebSocket Security 7 Scaling WebSocket Applications 8 WebSockets

GRASP — General Responsibility Assignment Software Patterns 7 Feature-based structure 5 Dependency Injection 4 Dependency Inversion 4 Why prefer composition over inheritance? 4 Layered Architecture 7 DI containers and the dependency-injector library 7 Monolith vs microservices 5 Clean Architecture 7 MVC pattern Hexagonal Architecture (Ports and Adapters) 7 Domain-Driven Design (DDD) 8 CQRS and Event Sourcing 8 Repository and Unit of Work Patterns 8 Event-Driven Architecture and Sagas 8 Transactional Outbox Pattern 6 Rate-Limiting Algorithms 7 Idempotency Keys (API-Level Deep Dive) 7 Event-Driven Architecture 5 The twelve-factor app

Service Discovery 4 Inter-service Communication 5 Distributed Tracing 5 Data Consistency Across Services 5 Service Mesh 5 API Gateway 5 Microservices — Common Interview Questions and Answers 4 Event-Driven Microservices 6 Resilience patterns for service-to-service calls Microservices Architecture

Sentry 5 Grafana 5 Prometheus 5 Datadog 7 ELK Stack (Elasticsearch, Logstash, Kibana) Jaeger 7 OpenTelemetry 7 The Three Pillars of Observability 7 Choosing an Observability Stack 6 Correlation IDs and Trace Context in Async Python 6 Sampling Strategies for Tracing 6 SLO, SLI, SLA, and Error Budgets 6 Structured logging in Python

Docker and Docker Compose Command Guide 3 Docker Image vs Container 3 Purpose of Containerization 3 Docker Image Layers 3 Docker Compose 3 Scaling containers 6 Docker network modes 5 Multi-stage builds 5 Volumes, bind mounts and tmpfs 5

Kubernetes Basics 5 Pods, Services, Deployments 5 ConfigMaps and Secrets 5 Probes and HPA 6 Ingress and Networking 6 Helm 5 Kubernetes — Common Interview Questions and Answers 4 Gateway API 6 Kubernetes

CloudFormation vs Terraform 3 Ansible 6 Terraform — State 6 Terraform — Modules and Composition 6 Terraform — Workspaces and Environment Strategy 5 Terraform — Plan/Apply Lifecycle, Drift, and Import 6 Terraform — Secrets, Testing, and CI/CD 6 OpenTofu and the Terraform licence split 5 Terraform

AWS Interview Essentials — Cross-Service Decision Matrices 6 AWS Glue Amazon Redshift Amazon Kinesis Amazon Athena AWS Analytics AWS SNS (Simple Notification Service) - Complete Guide SQS — Visibility Timeout, Consumer Patterns, and Failure Handling 7 AWS SQS (Simple Queue Service) - Interview Guide Amazon EventBridge AWS Step Functions AWS Application Integration AWS Cost Explorer AWS Cloud Financial Management Comparing AWS Compute Services Amazon EC2 AWS Fargate AWS Lambda AWS Compute Amazon ECR (Elastic Container Registry) ECS — Task Placement and Lifecycle 6 Amazon ECS (Elastic Container Service) Amazon EKS (Elastic Kubernetes Service) AWS Containers Aurora — Backtrack, Parallel Query, Data API, and Storage 5 Amazon Aurora Amazon DynamoDB ElastiCache — Failover, Serverless, and Operations 5 Amazon ElastiCache Amazon RDS (Relational Database Service) AWS Databases AWS CodeBuild AWS Developer Tools AWS Auto Scaling AWS CloudFormation CloudWatch — Cost Gotchas and Advanced Patterns 6 Amazon CloudWatch AWS SSM Parameter Store AWS Management and Governance API Gateway — Advanced Patterns, Templates, and Failure Modes 7 Amazon API Gateway Amazon CloudFront VPC — Troubleshooting and Cost Gotchas 6 Amazon VPC Elastic Load Balancing Amazon Route 53 AWS Networking and Content Delivery Amazon Cognito IAM — Advanced Role Patterns 6 AWS Identity and Access Management (IAM) Secrets Manager — Rotation, Version Stages, and Parameter Store Choice 6 AWS Secrets Manager AWS KMS (Key Management Service) AWS Security Identity and Compliance AWS Backup Amazon Elastic Block Store (EBS) Amazon Elastic File System (EFS) Amazon File Cache Amazon S3 (Simple Storage Service) AWS Storage Gateway AWS Storage

Azure for an AWS-shaped brain 4

GCP for an AWS-shaped brain 5 GKE in practice 6 Google Cloud

Git: the commands that get asked about 6 Merge vs Rebase 5 Interactive Rebase 6 reset, revert, checkout, restore 6 Reflog and Recovery 6 Bisect — Find the Commit That Broke It 5 Stash — Save Work Without Committing 6 Cherry-pick — Apply a Commit From Another Branch 6 Worktrees — Multiple Checkouts of One Repo 6 Branch Strategies 6 Pull Request Workflow 6 Merge Conflict Resolution 6 Git Hooks 6 Git Internals — Objects, Refs, the Real Storage 7 Dangerous Commands and Safety 7

Bash: triage and scripting 6 Bash Scripting Essentials 6 Quoting and Expansion 6 Parameter Expansion 6 Pipes, Redirects, File Descriptors 7 Exit Codes and Strict Mode 6 find and xargs 6 grep, sed, awk 7 Process Management 6 Signals and Traps 6 File Permissions and Ownership 6 SSH — Keys, Config, Tunnels 6 Cron and Systemd Timers 6 Systemd Services and Journalctl 7 Shell Startup, Environment, and PATH 6

Common data structures and their features Two pointers 4 Sliding window 4 Prefix sums 4 Counting, deduplication, and lookup with hash maps 4 Linked list basics — reverse, cycle detection, merge 4 Tree traversals — DFS and BFS 4 BSTs and tries 6 Graph algorithms — BFS, DFS, topological sort, union-find 4 Dijkstra's algorithm — shortest path in weighted graph 4 Dynamic programming — patterns and classic problems 2D dynamic programming 6 Recursion and backtracking 4 Binary search variants Python-specific patterns: bisect, heapq, deque Monotonic stack 6 Intervals 5 Greedy algorithms and bit manipulation 6 Data structures & algorithms

OWASP Top 10 (2021) SQL injection XSS and CSRF Password hashing OAuth 2.0 and OpenID Connect JWT pitfalls Secrets management and rate limiting Pickle, YAML, and Deserialization Attacks (Python-Specific) 6 SSRF and Command Injection 6 CORS — The Deep Dive 7

Formatters 4 Linters and static analysis 5 Type-Checking Strategy 6 Pre-commit Hooks and Code Review 6 Refactoring 6 Technical Debt and Complexity 6

CI/CD Basics 7 GitHub Actions 8 GitLab CI 7 Self-Hosted Runners 7 Deployment Strategies 7 Secrets and Supply Chain in CI 7 Pipeline Design Patterns 7 Progressive delivery on Kubernetes — Argo Rollouts & Flagger

OSI and TCP/IP Models 4 TCP vs UDP 5 IP Addressing, Subnets, CIDR 5 NAT (Network Address Translation) 5 DNS 5 Ports and Sockets 5 Firewalls and Security Groups 5 VPN 5 VPC and Cloud Networking 6 Load Balancers 6 Proxies: Forward vs Reverse 5 TLS, HTTPS, Certificates 6 CDN (Content Delivery Network) 6 Network Troubleshooting Tools 6 Ingress vs Egress Traffic 5 HTTPS Handshake, mTLS, Keepalive, and the Reverse-Proxy Edge 7 Computer Networking

Spark — Architecture, DAGs, and Execution 7 PySpark Gotchas and Databricks 7 Pandas — Fundamentals and Indexing 7 Pandas — groupby, merge, reshape 7 When Pandas Breaks Down — and What to Reach For 7 Polars — Lazy, Eager, and Expression API 7 Parquet — Columnar Format Fundamentals 7 Delta Lake — ACID Tables on Object Storage 7 Data mesh and federated architecture 5 ETL, orchestration, and dbt 6 Data catalogues, governance, and lineage 5 Data architecture

Market data 5 Backtesting 5 Backtesting libraries: vectorbt, Backtrader, QuantConnect 5 Portfolio optimization 5 Machine learning for finance 5 FIX protocol and market connectivity 5 Python performance for quantitative work 5 Risk and running a strategy in production 5 Quant and fintech

Healthcare data standards: HL7, FHIR, OMOP 6 PHI, privacy, and secure coding in regulated systems 5 GxP, computer system validation, and 21 CFR Part 11 5 Clinical document intelligence: protocol to structured workflow 6 Healthcare and regulated industries

Other domains

System design 30

Methodologies 9

Claude certification 8

Practical cases 3

System design / 07_worked_designs/

Worked designs

index source

This folder has no README. Everything inside it is listed below.

Notes

Worked Design — URL Shortener 5
Worked Design — Distributed Rate Limiter 6
Worked Design — Notification / Fan-out Service 6
Worked Design — News Feed / Timeline 6
Worked Design — Chat & Presence 6
Worked Design — Distributed Cache 7
Worked Design — Distributed Job Scheduler 7
Worked Design — Idempotent Payment Flow 6

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