Playground
There is no Python in a browser, so the honest version of a playground for this course is the three commands that give you one on your own machine. The scratchpad underneath is JavaScript, which the page really can run.
The real playground is one command
Python ships an interactive interpreter. Typing python3 with no arguments
gives you the >>> prompt, which evaluates as you type and is the fastest
way to answer "what does this actually do":
$ python3
Python 3.14.7 (main, Aug 5 2026, 10:29:49) [Clang 17.0.0] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 0.1 + 0.2
0.30000000000000004
>>> len("hello")
5
>>> exit()A transcript of an interactive session rather than a runnable panel: it is showing what your own terminal does, and there is no interpreter in this page to reproduce it. Everything it demonstrates is checked for real in the lessons.
For anything longer than a line or two, put it in a file and run that instead
(python3 scratch.py). And when a project needs a package, give it its own
environment first — lesson 21 covers exactly why, and what goes wrong when you skip it.
A JavaScript scratchpad, which does run here
Same runner the JavaScript panels in the lessons use, with the assertion helper already defined. It is here so there is something in the page itself to poke at.
const same = (a, b) => JSON.stringify(a) === JSON.stringify(b);
const test = (name, got, want) => console.log(
(same(got, want) ? 'ok ' : 'FAIL ') + name +
(same(got, want) ? '' : ` got ${JSON.stringify(got)}, want ${JSON.stringify(want)}`)
);
// Never use === on a computed float. See the lesson on numbers.
const close = (a, b, tol = 1e-9) => Math.abs(a - b) < tol;
// Try something. test(name, got, want) prints ok or FAIL.
const counts = (words) => words.reduce((acc, w) => {
acc[w] = (acc[w] || 0) + 1;
return acc;
}, {});
console.log(counts(['a', 'b', 'a']));
test('counting words', counts(['a', 'b', 'a']), { a: 2, b: 1 });Output