1,754 concepts written so farFree, no account
Pressentify is an interactive cheatsheet for the stack you actually ship on. Every concept comes three ways — a plain-English explanation, a worked example you can run, and a reference block you will come back to at 5pm on a Friday.
python / functions / default-arguments
Concept 41 of 468
A default argument is evaluated once, when the def line runs — not on each call. Give a function a mutable default and every call that omits the argument shares one object.
Gotcha. The list survives between calls, so results accumulate — a classic source of “works once, wrong after” bugs.
Why it reads differently
Most tutorials are readable once and useless afterwards; most references assume you already know the thing. This is the same page doing both jobs — and it is engineered to the same standard as the code it teaches.
Python executes in the page through WebAssembly — edit the snippet, run it, see the real output. Nothing to install, nothing sent to a server.
from collections import Counter
Counter("mississippi").most_common(2)
>>> [('i', 4), ('s', 4)]Every diagram is vector, themed from the same tokens as the page, and carries a written alternative — so it works in dark mode, in print, and in a screen reader.
One keystroke searches every concept in the topic and jumps to the exact anchor — not to the page it lives on.
Pick topics and an hours-per-week budget; get a dated schedule you can print.
Hide advanced material on the first pass, bring it back on the second. Level is never signalled by colour alone.
Prints properlyChrome hides, tabs unfold, diagrams swap to text.
Keyboard firstSkip link, visible focus, no mouse-only paths.
Contrast solvedEvery accent computed to 4.6:1, both themes.
No account neededNothing to sign up for, ever.
The library
8 topics are written and readable today. The other 6 are fully mapped — every section and concept is already planned, and each card shows exactly how much of it exists. No topic pretends to be finished.
beginner40+ hours
A readable, batteries-included language for backends, data work and automation.
Complete — 821 items39 sections
intermediate15+ hours
A relational database that keeps your data correct under pressure.
132 of 428 items covered75 sections
advanced15+ hours
How to shape systems that stay fast and available as they grow.
Complete — 290 items106 sections
intermediate40+ hours
A batteries-included Python web framework for database-backed applications.
1,112 of 1,442 items covered105 sections
intermediate15+ hours
A document database that stores flexible, JSON-shaped records.
158 of 482 items covered86 sections
intermediate12+ hours
Rent servers, storage and managed services instead of running your own.
Complete — 278 items70 sections
advanced25+ hours
Ship real features on top of models — RAG, agents, evaluation and inference.
63 of 659 items covered97 sections
beginner30+ hours
Pattern-based problem solving — arrays to graphs, for interviews and daily fundamentals.
67 of 341 items covered32 sections
How it works
There is no funnel here. The whole library is on the open web, indexed, printable, and readable without signing anything.
Thirteen tracks with prerequisites written down, so you can tell whether to start here or one level back.
Explain when it is new, Example when you want to see it work, Reference when you already know and just need the shape.
Questions at the end of a section, written against that section — so you find the gap here rather than in an interview.
Search it with one keystroke, print it, or leave the tab open. After the first read, the same page is your reference.
Also here
The same site runs a job board aggregator across hundreds of company career pages. It exists because the problem with job boards is not finding postings — it is that nine in ten of them are not for you, and you read all of them anyway.
Not hidden behind a filter you have to remember to set — removed, with a record of what went and why. Sales, HR, finance, legal and their managerial versions never reach the list.
Your whole résumé is read in — summary, roles, bullets, projects, education, skills — and shown back to you to correct before anything is saved. The file itself is never kept; what it says becomes a profile you can edit line by line.
Every posting and your profile become vectors, so a role can rank highly without sharing a single word with your CV — and one that repeats your keywords in a job you would hate does not.
Ask one posting whether it is worth twenty minutes and get reasons quoting the posting itself, plus the concerns — wrong level, salary below your floor, wrong city.
Fresh, not endlessPostings expire at 30 days. Anything you saved stays.
Saved searchesName a set of filters, come back to it tomorrow.
Filters that count honestlyEvery facet shows the whole set, never a truncated list.
Your CV is not keptIt is read, turned into skills you confirm, then dropped.
There is a demo account behind the door — one click, nothing to fill in.
2,921 of 9,188 mapped items are covered, across 1,754 written concepts — three topics finished end to end. No account, no paywall, no email box — open a topic and go.