Master Computer Scienceone written lesson at a time
1,647 in-depth lessons across 23 courses - from your first Python variable to distributed system design. Written to be read, not watched.
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Lists & Loops
4.3 · List Comprehensions
A comprehension is a loop and an if written as one expression. Once you can read one, you can read almost any Python codebase.
Start anywhere
Every course is complete and free to read today. No drip-feed, no paywall halfway through.
Or follow a route to a job
8 ordered tracks that stack courses in the sequence they actually build on each other.
Not sure which job you're aiming at?
Picking a course is hard when nobody has told you what the jobs are. So here is the inside of a normal tech company: 17 teams, what each one does on an ordinary Tuesday, and which of them will hire you with no experience.
How one feature travels
- 1Someone asks for it
- 2It gets drawn
- 3It gets built
- 4Someone tries to break it
- 5It goes live
- 6It has to keep working
- 7People find out and get help
Built to be read, not sat through
Written, not filmed
Skim it, search it, come back to the one paragraph you needed. No scrubbing a timeline to find the bit that mattered.
Diagrams that explain
Architectures, request flows and comparison matrices are drawn as clean diagrams - laid out by what they mean, not auto-generated spaghetti.
Nothing behind a wall
Every lesson in every course is open. Progress and certificates are the only things that ask you to sign in.
Pick a course and start reading
1,647 lessons are sitting there, finished and free. The hardest part is choosing the first one.