python-in-22-days

A zero-install Python course that runs real CPython in the browser via Pyodide — 25 daily lessons, every snippet verified against a local interpreter before it ships.

The problem

Learning Python usually stalls before line one: install an interpreter, pick an editor, fight PATH. Meanwhile the tutorials themselves are unverified — snippets rot and the learner ends up debugging the lesson.

This project removes both obstacles. Lessons run actual Python in the browser through Pyodide (CPython compiled to WebAssembly), and verify.py compiles and executes every snippet in the repository so a broken example never reaches a learner.

Quickstart

Static site, no build step. Lessons load with fetch, so serve over HTTP — file:// will not work.

git clone https://github.com/thanvish21/python-in-22-days.git
cd python-in-22-days
python3 -m http.server 8000
# open http://localhost:8000

Verify every lesson before publishing content:

python3 verify.py    # schema check + compile/run every snippet; exits non-zero on failure

Deploy to Vercel (vercel.json is committed: clean URLs, X-Content-Type-Options: nosniff, always-revalidate on /data/*), or serve the folder from GitHub Pages — the core course needs no server-side code at all.

How it works

• Real execution, client-side. js/pyrunner.js lazily loads Pyodide 0.26.2 from the jsDelivr CDN on first Run (10-20s cold start), then reuses the instance. stdout and stderr are captured per run and input() is wired to a browser prompt so input lessons work live.
• Runaway-loop watchdog. User code is executed under a sys.settrace guard with a 12-second wall-clock deadline, so an infinite loop raises a readable TimeoutError instead of freezing the tab. Tracebacks are filtered down to the learner's own frames.
• Progress and gating. State lives in localStorage (py25_progress_v1). Day 1 is always open; day N unlocks when day N-1 is done. Days 6, 11, 16 and 22 are gated behind a timed module test that must be passed at 70% or better (py25_tests_v1). Finishing a day fires a badge toast and increments the streak counter.
• Content pipeline. One JSON file per lesson (data/dayNN.json) with typed blocks (text, code, tip, quiz, tryit, example, …) and a closing challenge. verify.py walks every file, schema-checks it, and runs each snippet — including tryit starters and solutions — reporting input-driven snippets as warnings.

index.html          app shell
js/pyrunner.js      Pyodide loader, stdout capture, 12s watchdog, traceback cleanup
js/render.js        lesson JSON -> interactive DOM
js/app.js           hash router, progress, day unlock, badges
js/course.js        module outline, timed module tests, PCEP exam-map page
js/ai-tutor.js      "PyBuddy" chat panel (see Status below)
api/run.js          Vercel function: run code via Judge0 (used by the advanced track)
api/grade.js        Vercel function: hidden-test grading, never leaks expectations
api/_judge0.js      shared Judge0 submit/poll/normalize helper
data/manifest.json  the day list
data/dayNN.json     one lesson per file, 25 files
data/modules.json   PCEP module grouping + module-test question banks
matrix/             advanced "1% HFT Matrix" track (own README + data/SCHEMA.md)
test/headless.html  manual smoke page for the Pyodide runner
verify.py           schema + compile/run check for every lesson

Course shape. 25 lessons from print() and variables through loops, collections, functions, error handling, files, modules, classes, comprehensions, pip, and a capstone. data/modules.json groups them into the module layout used by the PCEP-30-02 exam map, and the module tests use its question banks.

Advanced track. matrix/ is a separate four-tier systems-Python curriculum — async network foundations, memory management, metaprogramming and hooks, and GIL escape / native extensions — with 18 graded problems. Tiers 1-3 quick-runs work in Pyodide; tier-4 native work and the profiling harness need the Judge0-backed serverless functions (window.HFT_RUNNER_URL, default /api).

Configuration

Variable	Used by	Notes
JUDGE0_URL	api/run.js, api/grade.js	Judge0 instance for the advanced track
JUDGE0_KEY, JUDGE0_HOST	same	RapidAPI only
JUDGE0_LANG_PYTHON	same	Judge0 language id, default 71

Tech stack

Vanilla HTML/CSS/JavaScript with no framework, bundler or npm dependencies · Pyodide 0.26.2 (CPython on WebAssembly) · Vercel Node serverless functions (@vercel/node@3.2.0) · Judge0 for the advanced track · Python 3 for the offline verifier.

Status and known gaps

• The curriculum is 25 days, not 22 — the repository name predates the expansion.
• The AI tutor panel is not functional as shipped. js/ai-tutor.js posts a proxy-shaped body straight to https://openrouter.ai/api/v1/chat/completions with no credentials, and this repo contains no api/tutor.js to receive it. Wiring it up means adding that serverless proxy (as done in the sibling Java repo) and pointing the client at it.
• Pyodide is fetched from a CDN, so the first Run needs a network connection and takes 10-20 seconds; only pure-Python standard-library code is guaranteed to work.
• Progress is per-browser localStorage — no accounts or sync.
• test/headless.html is a manual smoke page, not an automated test suite.

License

MIT — see LICENSE.