CodeForge

A desktop app for learning to program and then grinding coding-interview problems — built for a Codility screen, useful for any of them.

Switch the programming language inside the app. Python, JavaScript, Java, C#, Go, Rust and C++ all work: you get the same problem, starter code generated for that language's type system, and your solution is compiled and graded by the real toolchain.

English, German, French and Spanish. The flag button switches the whole interface, plus every multi-language problem statement, hint and note. The Python-only curriculum and drills are English and German; anything without a translation falls back to English rather than breaking.

Written in Python with zero third-party dependencies — standard library and tkinter only. Nothing to pip install.

Die ganze App gibt es auf Deutsch, und die Programmiersprache lässt sich direkt in der App umschalten. · Toute l'application existe aussi en français. · La aplicación completa también está en español.

Where it goes next is written up in ROADMAP.md, along with the things worth knowing before changing anything.

Download

Get the latest build from the Releases page — Windows x64, Linux x64 and macOS (Apple Silicon). Unpack and run CodeForge. No Python needed; the app carries its own interpreter.

On an Intel Mac, build it yourself (one command, see below) — GitHub is retiring its Intel macOS runners, so there is no prebuilt x86_64 archive.

To use a language other than Python

Python is built in. The others run your code with the real toolchain, so it has to be on your machine — the language dropdown shows a ✓ next to the ones it found:

Language	Needs
Python	nothing, it is bundled
JavaScript	Node.js
Java	a JDK (javac + java)
C#	the .NET SDK
Go	the Go toolchain
Rust	rustc (via rustup)
C++	g++, clang++, or Visual Studio

Nothing is downloaded at runtime and no network is used.

What's inside

Learn — a course in every language

• Python: 17 lessons. Theory written for someone who has not programmed before, but with the interview-relevant detail included (why x in set beats x in list, why list.pop(0) is O(n), why mutable default arguments bite).
• Every other language: 4 lessons covering the syntax you need to read anything, the collection you will reach for constantly, the language's own defining idea — Java's classes, C#'s LINQ, Go's multiple returns and errors, Rust's ownership and borrowing, C++'s references and <algorithm>, JavaScript's closures — and the string handling interview questions actually demand.

Every lesson has an editable, runnable example program and a graded exercise with staged hints. Both the examples and the exercises are executed by that language's real toolchain.

Practice — randomised drills in every language

Every drill is a generator: pick a topic, press the button, and you get a fresh statement with different numbers, different words and freshly computed tests. Grind one concept twenty times without ever replaying a memorised answer.

Python has 31 generators; the other six languages share a portable set of 6. The randomised parameter is baked into the reference solution for each language, so the drill is genuinely re-generated rather than translated.

Interview — problems in every language

• 28 multi-language problems — one statement, generated starter code, and a reference solution in all seven languages. Two Sum, Kadane, binary search, sliding window, two pointers, hash maps, prefix sums, bit tricks, the sieve of Eratosthenes, matrices — plus Codility's BinaryGap, PassingCars, CyclicRotation, Dominator, OddOccurrencesInArray and TapeEquilibrium.
• 64 more when Python is selected — the complete Codility lesson set (BinaryGap, MaxCounters, TapeEquilibrium, GenomicRangeQuery, Fish, StoneWall, Dominator …) plus the LeetCode patterns that keep coming up.

Hidden tests run on submit, including deliberately large inputs so an O(n²) answer fails instead of quietly passing.

Playground — in every language

Free editor with an stdin box, so you can practise the read-from-stdin style of judge exactly as Codility runs it. Each language starts you with the same small program — read stdin, print something formatted, loop — so switching language shows you the same thing written idiomatically elsewhere.

Progress

XP, levels, day streak, per-topic breakdown, 14-day chart — in progress.json, local.

How other languages are graded

There is no JSON parser in the harness, because Java, Rust and C++ do not ship one. Instead each task declares a type signature, and the backend renders the test cases as native literals of the target language, generates a harness that compares the results itself, and prints one line per case in a tiny text protocol:

@@CF|0|PASS
@@CF|1|FAIL|[1, 3]|[0, 1]
@@CFEND

The same signature generates the starter code, so sum_range is nums: &[i64] -> i64 in Rust, long[] -> long in Java and []int -> int in Go without anything being written twice.

The editor

Syntax highlighting, line numbers, auto-indent, bracket completion, Tab/Shift+Tab block indent, Ctrl+/ comment toggle, Ctrl+D duplicate line, undo/redo. Your code runs in a separate process with a timeout, so an infinite loop kills the sandbox and not the app.

Key	Does
Ctrl+Enter	run tests
Ctrl+1..5	switch tab
Tab / Shift+Tab	indent / dedent
Ctrl+/	toggle comment
Ctrl+D	duplicate line

Run from source

python app.py

Python 3.9+ with tkinter (Debian/Ubuntu: sudo apt install python3-tk).

Build it yourself

pip install pyinstaller && pyinstaller --noconfirm CodeForge.spec

Then check the packaged build can still execute user code — a frozen app has no python.exe beside it, so CodeForge relaunches its own executable as the interpreter:

python tools/verify_frozen.py

Tests

Content is verified, not assumed.

python selftest.py 3 en     # Python lessons, drills and problems
python selftest.py 3 de     # ... and German, plus translation coverage
python selftest_multi.py    # every reference solution in every installed language
python tools/gui_smoke.py   # builds the UI, walks every tab and every language

selftest_multi.py skips languages whose toolchain is missing instead of failing, so it is useful on any machine.

Layout

File	Purpose
app.py	window, sidebar, the five tabs
theme.py	palette, fonts, flat widgets, the hand-drawn flags
editor.py	code editor and output console
taskview.py	the shared "solve a task" panel
languages/	one execution backend per programming language
problems_multi.py	problems that work in every language
lessons_multi.py	the short course for each non-Python language
drills_multi.py	randomised drill generators that work in every language
curriculum.py	one interface over both kinds of course
languages/playground.py	the starter program and build/run recipe per language
problems.py · problems_de.py	the Python-only interview bank
lessons.py · lessons_de.py	the Python curriculum
drills.py	randomised generators (German inline — they interpolate values)
runner.py	the Python-only subprocess runner
i18n.py	interface language (EN/DE/FR/ES), topic and difficulty names
problems_multi_i18n.py	French and Spanish text for the multi-language bank
progress.py	XP, streaks and preferences

Adding a language

Implement languages/base.Backend: probe() to detect the toolchain, type_name() and literal() to render values, starter() and harness() to generate code, and run() to build and execute. Register it in languages/__init__.py, add solutions to the problems in problems_multi.py, and run python selftest_multi.py <your-language>.