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Fastify — Node Web Framework

Fastify is a high-performance Node.js web framework with schema-driven validation, plugin encapsulation, hooks, decorators, and built-in Pino logging — covering routes, plugins, hooks, error handling, and production hardening.
javascript node backend framework fastify web

node:fs — File System

Node.js file system module — the three APIs (callback, sync, promises), reading and writing files, directory operations, watchers, atomic writes, and path module pairing.
javascript node filesystem fs language

node:stream — Streams

Node.js streams — Readable, Writable, Duplex, and Transform, the modern pipeline() API, backpressure, async iterators, Web Streams interop, and patterns for piping files, HTTP bodies, and gzip compression.
javascript node streams pipeline language

PCRE — Perl Compatible Regular Expressions

PCRE2 syntax reference — character classes, quantifiers, anchors, groups, lookarounds, backreferences, flags, and advanced features used in grep, sed, nginx, PHP, and dozens of other tools.
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Design Patterns — Gang-of-Four Essentials and Modern Variants

A practical reference for classic OOP design patterns — Strategy, Observer, Factory, Adapter, Decorator, Repository — with examples in Python, TypeScript, and Go.
design-patterns oop architecture gof refactoring principles

SOLID — Five Principles for Maintainable OO Design

A modern walk-through of the SOLID principles — single responsibility, open-closed, Liskov, interface segregation, dependency inversion — with anti-examples and refactors in TypeScript and Python.
solid oop principles srp ocp lsp isp dip refactoring architecture

argparse — Stdlib CLI Argument Parser

Parse command-line arguments with Python's stdlib argparse module. Covers positional/optional args, subparsers, nargs, validation, mutually exclusive groups, FileType, env-var fallbacks, and argcomplete.
python stdlib cli scripting tooling

dataclasses — Boilerplate-Free Classes

Define typed data containers with @dataclass — frozen, slots, kw_only, default_factory, __post_init__, asdict, replace, and how it compares to attrs, pydantic, NamedTuple, TypedDict.
python stdlib typing

datetime — Dates, Times, Timezones

Work with dates, times, and timezones in Python using the stdlib datetime module and zoneinfo. Covers aware vs naive datetimes, ISO-8601 parsing, strftime/strptime, timedelta arithmetic, and DST handling.
python stdlib time timezones parsing data

Essential Python Packages

Overview of the 34 most useful Python packages — HTTP clients, data science, web frameworks, orchestration, testing, and tooling. Each has its own dedicated page with examples.
python packages pip overview

fastapi — Fast ASGI API Framework

Build high-performance async REST APIs with FastAPI. Covers path params, request bodies, Pydantic models, dependency injection, and auto-generated OpenAPI docs.
python fastapi api async asgi rest openapi pydantic

flask — Micro Web Framework

Build lightweight web apps and REST APIs with Flask. Covers routes, request handling, JSON responses, blueprints, and the debug-server warning.
python flask web api wsgi microframework

httpx — Modern HTTP Client

Make sync and async HTTP requests with httpx. Covers GET/POST, async usage, HTTP/2, streaming, and how it compares to requests.
python httpx http api async networking

Python Installation — Quick-Pick

Choose your OS and get Python installed in minutes. Covers Windows, WSL/Ubuntu, macOS, and Linux with recommended versions and verification steps.
python install

Python Installation — Linux

Install Python 3 on Debian/Ubuntu, Fedora/RHEL, and Arch Linux. Covers package managers, pyenv, and building from source for unsupported distros.
python install linux debian ubuntu fedora arch pyenv

Python Installation — macOS

Install Python 3 on macOS via Homebrew or pyenv. Explains the system-Python warning, PATH precedence, and verification steps.
python install macos homebrew pyenv

Python Installation — Windows

Install Python 3 on Windows via winget or the python.org installer. Covers PATH setup, the py launcher, and verification steps.
python install windows

Python Installation — WSL Ubuntu

Install Python 3 inside WSL2/Ubuntu via apt, the deadsnakes PPA, or pyenv. Covers the python3-venv quirk and version aliasing.
python install wsl ubuntu linux

itertools & functools — Functional Toolbelt

The two stdlib modules every Python developer pairs together — iterator algebra (chain, groupby, batched, pairwise) and function plumbing (lru_cache, partial, reduce, singledispatch, cached_property).
python stdlib functional itertools functools

json — Stdlib JSON Encoder/Decoder

Encode and decode JSON in Python with the stdlib json module. Covers dumps/loads, indent/sort_keys/separators, custom default= and JSONEncoder, object_hook decoding, JSONL streaming, and orjson/ujson/msgspec comparison.
python stdlib json data serialization parsing

logging — Stdlib Logging

Configure Python's built-in logging module — loggers, handlers, formatters, dictConfig, rotation, structured records, and how it compares to loguru.
python stdlib logging

pdb — Python Debugger

Pause, inspect, and step through Python programs with pdb. Covers breakpoint(), command reference, post-mortem debugging, conditional breakpoints, and enhanced alternatives like ipdb, pdbpp, and pudb.
python pdb debugging stdlib repl tooling

poetry — Dependency Management & Packaging

Manage Python project dependencies, virtual environments, and package publishing with Poetry. Covers pyproject.toml, lockfiles, groups, and publishing to PyPI.
python poetry packaging dependencies pyproject lockfile

pre-commit — Git Hooks for Linters and Formatters

Run linters, formatters, and validators automatically on every git commit. Covers .pre-commit-config.yaml, essential hooks (ruff, mypy, check-yaml), autoupdate, and CI integration.
python pre-commit git-hooks workflow ci code-quality tooling

pydantic — Data Validation

Validate and parse data at runtime using Python type hints with Pydantic v2. Covers BaseModel, field validators, nested models, and JSON serialization.
python pydantic validation types models serialization

pyproject.toml — Modern Python Project Config

The canonical config file for modern Python projects — [project] metadata, [build-system] backends (setuptools, hatchling, pdm-backend, poetry-core, flit-core), [tool.*] sections, dynamic versioning, scripts, building, and publishing.
python packaging pyproject toml build pep-621

re — Python Regular Expressions

Python's built-in regex module — compile vs not, match/search/findall/finditer/sub, named groups, lookarounds, verbose mode (re.X), and how it differs from PCRE.
python stdlib regex re patterns

requests — HTTP for Humans

Make HTTP requests in Python with the requests library. Covers GET/POST, JSON, sessions, authentication, retries, and common pitfalls.
python requests http api networking

scikit-learn — Classical Machine Learning

Build classical ML pipelines with scikit-learn. Covers the estimator API, train_test_split, Pipeline, ColumnTransformer, cross-validation, metrics, and model persistence.
python scikit-learn ml data-science pipelines modeling classification

streamlit — Data Apps in Pure Python

Build interactive web apps for data and ML in pure Python. Covers widgets, layout, session state, caching, multipage apps, and deployment patterns.
python streamlit ui dataviz prototyping web frontend

subprocess — Spawning Processes

Run external commands from Python with subprocess. Covers run vs Popen, capture_output, streaming, pipes, timeouts, env/cwd overrides, and shlex quoting safety.
python stdlib shell

typing — Advanced Type Hints

Go beyond list[int] and str | None. Covers Protocol, TypeVar bounds, ParamSpec, Concatenate, Self, Annotated, TypedDict with NotRequired/Required, TypeAlias, TypeGuard, TypeIs, cast, assert_type, and reveal_type.
python typing types stdlib mypy generics protocol

uv — Fast Python Package Manager

Install packages and manage virtual environments blazingly fast with uv. Covers uv pip, uv venv, uv run, uv init, and how it compares to pip and poetry.
python uv pip packaging venv tools astral

Virtual Environments — venv

Create, activate, and manage Python virtual environments with venv. Covers activation for every shell, pip usage, requirements files, and cleanup.
python venv virtualenv pip packaging

Branded Types — Nominal Typing in a Structural System

Branded (a.k.a. nominal, opaque, tagged) types add a phantom marker to a primitive so the compiler refuses to mix two strings — useful for IDs, units, validated input, and money. Covers hand-rolled brands, type-fest's Opaque/Tagged, Zod's .brand(), class-based brands, and runtime validation pairings.
typescript types patterns language branded

Declaration Merging — Interfaces, Namespaces, Modules, Globals

Deep dive into TypeScript declaration merging — interface merging, namespace + class, namespace + function, module augmentation, global augmentation, and the Express Request pattern.
typescript declarations modules patterns advanced

Discriminated Unions — Tagged Variants & Exhaustiveness

Discriminated unions model finite states with a shared literal tag, enabling exhaustive narrowing in switch statements, Result-style error handling, reducer actions, and pattern-matched API responses.
typescript types patterns narrowing language

.d.ts Files — Ambient Declarations, Asset Imports, Module Typing

Authoring .d.ts files — ambient declarations, declare module 'foo', asset typing (*.svg?raw), declare global, triple-slash refs, and the home-hero.svg?raw pattern used in this project.
typescript declarations modules ambient dts

infer Keyword — Extracting types from patterns

TypeScript's infer keyword declares a fresh type variable inside a conditional type, letting you pull a sub-type out of a matched shape. It powers ReturnType, Parameters, Awaited, and most advanced type extractors.
typescript types advanced language

satisfies Operator — Type-check without widening

TypeScript's satisfies operator checks a value against a type while preserving its narrow literal inferred type. The middle ground between an annotation that widens and an as cast that lies.
typescript types operators language

Structural Typing — Duck Typing at the Type Level

Understand TypeScript's structural type system — assignability is based on shape, not name; excess property checks are the one exception; nominal typing requires branded types or class privates.
typescript types concepts language

Template Literal Types — String Algebra at the Type Level

Template literal types let TypeScript pattern-match and synthesize string types — covering Uppercase/Lowercase intrinsics, infer-based parsers (Split, Join, CamelCase), route-param extraction, JSON path keys, and typed i18n helpers.
typescript types advanced template-literals language

TypeScript Modules — module, moduleResolution, .mts / .cts

Deep dive into TypeScript's module system — module/moduleResolution pairs, .mts/.cts file extensions, NodeNext vs Bundler resolution, paths, and tsconfig extends.
typescript modules esm nodenext tooling

typeof & keyof — Type-level operators

TypeScript's typeof promotes a runtime value into the type position; keyof extracts the union of property keys. Together they form the backbone of type-safe lookups, enum-from-object patterns, and inferred shapes.
typescript types operators language

Sentence Transformers — Embeddings, Search & Fine-Tuning

Comprehensive reference for the sentence-transformers Python library — embeddings, similarity, clustering, retrieval, fine-tuning, and popular models (BGE, E5, GTE, Nomic, Jina).
python embeddings nlp sentence-transformers semantic-search vector-db rag clustering fine-tuning bge e5 gte nomic jina

AutoGen — Multi-Agent Conversations

Build multi-agent AI systems with Microsoft AutoGen. Covers agents, group chats, code execution, tool registration, async runtimes, and LLM configuration.
python autogen agents llm ai microsoft multi-agent code-execution

ChromaDB — Embedded Vector Database

Store and query vector embeddings locally or over a network with ChromaDB. Covers client types, collections, add, query, metadata filters, embedding functions, and LangChain/LlamaIndex integration.
python chromadb vector-database embeddings rag ai similarity-search

crewAI — Role-Based Agent Crews

Orchestrate teams of role-playing AI agents with crewAI. Covers agents, tasks, crews, tools, LLM selection, memory, YAML config, and the kickoff lifecycle.
python crewai agents llm ai multi-agent rag tools

google-generativeai — Gemini SDK

Call Google's Gemini models from Python for text, multimodal, streaming, chat, function calling, and embeddings. Covers the genai SDK, safety settings, file API, and async usage.
python google gemini llm ai multimodal api

guidance — Constrained LLM Generation

Interleave Python control flow with LLM generation and enforce structured output using guidance. Covers gen(), select(), chat blocks, regex constraints, JSON schemas, and token healing.
python guidance llm ai structured-output constrained-generation transformers

LangChain — LLM Application Framework

Build LLM-powered pipelines with LangChain. Covers LCEL chains, chat models, prompts, output parsers, tools, agents, retrievers, memory, and streaming.
python langchain llm ai rag agents openai anthropic

LlamaIndex — Data Framework for LLMs

Build RAG pipelines and LLM-powered data applications with LlamaIndex. Covers document loading, indexing, query engines, custom LLMs and embeddings, persistent storage, and agents.
python llamaindex llm rag ai embeddings agents retrieval

notebooklm-py — Unofficial NotebookLM Client

Automate Google NotebookLM from Python with the unofficial notebooklm-py library. Covers authentication, notebook and source management, summaries, FAQ generation, and audio podcast creation.
python notebooklm google ai automation unofficial

transformers — Hugging Face

Load and run pre-trained models for NLP, vision, and audio with the Hugging Face Transformers library. Covers pipelines, AutoModel, tokenisation, generation, fine-tuning, and device placement.
python huggingface transformers llm nlp ml pytorch

dagster — Modern Data Orchestration

Build, schedule, and observe data pipelines as software-defined assets with Dagster. Covers assets, jobs, schedules, sensors, resources, partitions, and the Dagster UI.
python dagster orchestration data pipelines assets etl mlops

DuckDB — Embedded Analytics Database

Run fast analytical SQL queries in-process with DuckDB. Covers Python API, CSV/Parquet ingestion, pandas interop, Arrow, window functions, and persistent databases.
python duckdb sql analytics olap parquet pandas arrow

litestar — High-Performance ASGI Framework

Build fast, type-safe HTTP APIs and web apps with Litestar. Covers route handlers, path/query/body params, DTOs, dependency injection, middleware, WebSockets, and OpenAPI.
python litestar asgi api web fastapi openapi rest

modin — Drop-in pandas at Scale

Speed up pandas workloads across all CPU cores with a one-line import swap. Covers Ray and Dask backends, config tuning, pandas interop, and when modin wins vs polars.
python modin pandas dataframes parallel ray dask data

polars — Fast DataFrames

High-performance DataFrames with a lazy expression API. Covers read/write, select, filter, group_by, joins, LazyFrame, datetime, string operations, and pandas interop.
python polars dataframes data csv parquet sql

prefect — Workflow Orchestration

Build, schedule, and observe Python workflows with Prefect. Covers flows, tasks, retries, schedules, deployments, caching, concurrency, and Prefect Cloud.
python prefect orchestration workflows scheduling etl pipelines

reflex — Full-Stack Web Apps in Pure Python

Build interactive web applications entirely in Python with Reflex. Covers state, components, events, pages, database, forms, and deployment.
python reflex web fullstack react ui components state

SQLModel — Typed ORM for FastAPI

Define database models with Python type hints using SQLModel. Covers table creation, CRUD, relationships, FastAPI integration, Pydantic validation, and async sessions.
python sqlmodel orm sql fastapi pydantic sqlalchemy database

tqdm — Progress Bars

Add auto-updating progress bars to any Python loop or CLI pipeline with tqdm. Covers iterables, manual updates, pandas integration, nested bars, async, Jupyter, and byte-piping.
python tqdm progress cli jupyter async

typer — CLI Apps with Type Hints

Build command-line interfaces using Python type annotations with Typer. Covers commands, options, arguments, subcommands, callbacks, rich output, and testing.
python typer cli argparse click terminal

JavaScript

Node.js runtime, package managers, async patterns, array methods, and frontend tooling — a complete JavaScript reference for the command line and the browser.
javascript node npm cli

Array Methods

JavaScript arrays have ~30 built-in methods for transforming, searching, and reducing data. Covers mutation, non-mutation, search, boolean, iteration, and static methods with real examples.
javascript arrays language

Async / Await

async/await syntax, error handling, parallel execution with Promise.all, sequential vs parallel loops, top-level await, AbortController, and common mistakes.
javascript async promises language

Error Handling

JavaScript error handling with try/catch/finally, built-in error types, custom error classes, error chaining with cause (ES2022), async errors, and practical patterns like result objects.
javascript errors language

Fetch API

The browser and Node 18+ built-in HTTP client that returns Promises. Covers GET/POST/PUT/DELETE, headers, error handling, streaming, AbortController, uploads, credentials, and CORS.
javascript fetch http api language

JavaScript Modules

CommonJS vs ES Modules in Node.js — syntax, how Node chooses the module system, dynamic import, top-level await, CJS/ESM interop, and common pitfalls.
javascript modules esm commonjs node

Node.js Runtime

How to use the Node.js runtime — REPL, running scripts, CLI flags, ESM vs CJS modules, built-in node: modules, the process object, and modern globals like fetch and structuredClone.
javascript node runtime cli esm cjs modules

Promises

JavaScript Promises represent the eventual completion or failure of an async operation. Covers states, chaining, combinators, callback conversion, AbortController, and common anti-patterns.
javascript promises async language

Regular Expressions

JavaScript has built-in RegExp support (ES2018+ with named groups, lookbehind, dotAll). Covers literal syntax, flags, character classes, methods, named captures, and common patterns.
javascript regex language

Programming

A reference hub for programming languages and their ecosystems — Python, JavaScript, and TypeScript, with package managers, runtimes, and tooling.
programming python javascript typescript overview

pip — Python Package Installer

Complete pip reference covering installation, package management, requirements files, private registries, caching, offline installs, and reproducible builds.
python pip packages cli packaging

TypeScript

Static typing for JavaScript — tsconfig reference, the full type system, generics, utility types, narrowing, and common compiler errors explained.
typescript javascript types

Common TypeScript Errors

A reference for the most frequent TypeScript compiler errors — their meaning, a minimal reproduction, and the correct fix. Covers TS2304, TS2345, TS2339, TS2322, TS2532, TS2554, TS2307, TS2366, TS7006, TS2571, TS2769, TS2693, plus type assertions and ts-expect-error.
typescript errors debugging language

Decorators

TypeScript decorators annotate and transform classes and class members. Covers the TC39 stage-3 standard decorators (TS 5.0+), legacy experimentalDecorators, decorator factories, method/class/field decorators, and reflect-metadata for NestJS and Angular patterns.
typescript decorators language

Enums

TypeScript enums create named constant sets as real runtime objects. Covers numeric, string, and const enums; reverse mapping; enum pitfalls; and when to prefer a union of string literals instead.
typescript enums language

Generics

TypeScript generics allow writing reusable, type-safe code that works over many types. Covers generic functions, interfaces, classes, constraints, keyof, conditional types, and the infer keyword.
typescript generics language

Mapped & Conditional Types

Mapped types iterate over type keys to create new types; conditional types pick between types based on a condition. Together they power all built-in utility types and advanced type composition.
typescript mapped-types conditional-types language

Type Narrowing

TypeScript narrowing refines broad types to specific ones within code branches. Covers typeof, instanceof, in, equality, assignment narrowing, discriminated unions, control flow analysis, and the never type.
typescript narrowing type-guards language

Type Guards

User-defined type guards narrow types at runtime using the `is` predicate, assertion functions, generic guards, and class-based patterns. Covers API validation, DOM guards, and when to use Zod.
typescript type-guards narrowing language

Type-Only Imports & Exports

import type and export type erase at compile time, preventing runtime side-effects and enabling better tree-shaking. Covers inline type qualifiers, verbatimModuleSyntax, and common gotchas with enums and namespaces.
typescript imports modules language

Types vs Interfaces

TypeScript has two ways to define object shapes — type aliases and interface declarations. Learn when each is appropriate, how they differ in extension, merging, and composability.
typescript types interfaces language

Utility Types

TypeScript's built-in generic utility types that transform existing types into new ones. Covers Partial, Required, Readonly, Record, Pick, Omit, Exclude, Extract, ReturnType, Awaited, and more.
typescript utility-types language

Python

Installation guides, essential packages, CLI snippets, and real-world recipes for Python 3.
python overview

asyncio — Async I/O

Write concurrent Python code with asyncio. Covers coroutines, asyncio.run, gather, create_task, timeouts, queues, and avoiding the blocking-call pitfall.
python asyncio async await concurrency coroutines

black — Python Code Formatter

Format Python code consistently with black. Covers installation, configuration, editor integration, and how it compares to ruff format.
python black formatting code-quality tools

Python CLI Snippets

Short standalone Python scripts for common tasks — file I/O, JSON manipulation, HTTP requests, CSV processing, and data transformation.
python snippets cli scripts json csv http file-io

click — CLI Builder

Build command-line interfaces with click using decorators. Covers commands, options, arguments, groups, prompts, and progress bars.
python click cli argparse terminal commands

django — Full-Stack Web Framework

Build database-driven web applications with Django. Covers project setup, models, migrations, the admin panel, views, forms, class-based views, middleware, signals, ORM advanced patterns, and the management command workflow.
python django web orm wsgi framework admin

jupyter — Interactive Notebooks

Run interactive Python notebooks with Jupyter. Covers JupyterLab setup, cell types, keyboard shortcuts, magic commands, nbconvert export, and common pitfalls.
python jupyter notebooks data analysis interactive

loguru — Structured Logging

Add structured, colorized logging to Python apps with loguru. Covers sinks, log levels, file rotation, retention, exception catching, and context binding.
python loguru logging debugging structured-logging

matplotlib — Plotting

Create publication-quality 2-D plots with matplotlib. Covers pyplot basics, subplots, savefig, common chart types, and the show-vs-save pitfall.
python matplotlib plotting visualization charts graphs

mypy — Static Type Checker

Catch type errors before runtime with mypy. Covers strict mode, common error codes, type: ignore annotations, gradual typing, and pyproject.toml configuration.
python mypy typing types static-analysis type-hints

numpy — Numerical Arrays

Create and manipulate N-dimensional arrays with NumPy. Covers array creation, broadcasting, vectorized math, indexing, and matrix operations.
python numpy arrays math data scientific

Python One-Liners

Useful Python one-liners runnable directly from the shell with python -c or python -m. No file creation needed.
python oneliners cli shell snippets

pandas — DataFrames

Load, filter, transform, and aggregate tabular data with pandas. Covers DataFrame creation, read_csv, groupby, merge, and the SettingWithCopy pitfall.
python pandas dataframes data csv analysis

pathlib — Object-Oriented File Paths

Work with filesystem paths using Python's built-in pathlib module. Covers Path creation, navigation, reading/writing files, glob patterns, and stat.
python pathlib files filesystem stdlib paths

Pillow — Image Processing

Open, resize, crop, convert, and save images with Pillow (PIL fork). Covers format conversion, filters, drawing, and EXIF handling.
python pillow pil images imaging graphics

pytest — Testing Framework

Write and run Python tests with pytest. Covers test discovery, assertions, fixtures, parametrize, conftest, and common patterns.
python pytest testing fixtures parametrize tdd

rich — Beautiful Terminal Output

Make terminal output beautiful with Rich. Covers styled print, Console, tables, progress bars, syntax highlighting, live displays, and the rich-cli command.
python rich terminal tui cli colors progress tables

ruff — Fast Linter & Formatter

Lint and format Python code with ruff — a single Rust-powered tool that replaces flake8, isort, and black. Covers configuration, rule selection, and CI usage.
python ruff linting formatting code-quality tools

scipy — Scientific Computing

Statistical distributions, optimization, integration, signal processing, and linear algebra with SciPy. Builds on NumPy arrays.
python scipy statistics optimization scientific math

sqlalchemy — SQL Toolkit & ORM

Connect to databases, write queries, and define ORM models with SQLAlchemy 2.0. Covers the engine, sessions, Core queries, ORM declarative models, relationships, session lifecycle, migrations with Alembic, and connection pool configuration.
python sqlalchemy orm sql database sqlite postgres