A wiki that grows by one lesson a day. Each lesson teaches one idea properly, and every term in it links to its own note, so reading one page leads to the next. Hover over a link to preview it.
Today
#2 · Python's object model: what a Python variable really is, and why changing one list can change another. Today’s puzzle: Contains Duplicate.
Earlier: #1 · The event loop
How to read it
- Start with the newest lesson. It takes 20-30 minutes.
- Follow the links you don’t know yet. Every concept note stands on its own.
- Answer the Check yourself questions before you open them. Testing yourself is what makes it stick; rereading doesn’t.
Tracks
| Track | What it covers |
|---|---|
| JavaScript | The event loop, closures, React, TypeScript, Node.js, web security |
| Python & Data | Python internals, SQL in depth, pandas, testing, pipelines |
| ML & Data Science | From linear regression to models in production |
| LLMs & RAG | Tokens, embeddings, retrieval, agents, evaluation |
| Backend & System Design | HTTP, APIs, caching, queues, scaling, consistency |
| CS Fundamentals | Complexity, memory, concurrency, networking, Git |
About
Written with Claude from primary sources (specs, RFCs, official docs), with code checked by running it. See about for how it is made and what it may get wrong.