Runnable, tested solutions for Day 54 of Udemy's "100 Days of Code: The Complete Python Pro Bootcamp": a first Flask server, the command line, __name__ and __main__, functions as first-class objects, and decorators. It is written for fellow course participants and for visitors who want a readable example.

🧭 Overview

The repository holds one small module per lecture step.

Folder	What it holds
`src/flask_day_54/`	The lecture code in four layers: `domain`, `application`, `infrastructure`, `presentation` (see ADR-0001); each layer keeps its constants in `constants.py`
`tests/`	pytest tests: `unit/` for `domain` and `application`, `e2e/` for the Flask application
`docs/`	Project documents, the screenshots in `docs/images/` and the wiki sources in `docs/wiki/`

Doxygen comments in the source describe every public name; Doxyfile builds them into docs/doxygen/.

The wiki (English, Danish and Bahasa Malaysia) explains what each lecture taught; its sources are in docs/wiki/ and are published to the repository wiki when they are merged to main.

Lecture steps

Each lecture has its own screenshot in docs/images/ (made by docs/images/capture.py with a headless browser, so no window opens on your desktop) and a wiki page that explains what the lecture taught.

Lecture 1: frontend, backend and the request-response cycle. The client asks, the Flask server prepares the answer, the database supplies data.

Lecture 2: the first Flask server. hello.py serves "Hello, World!" from the home route. Start it with flask --app flask_day_54.presentation.hello run (or set FLASK_APP: export FLASK_APP=flask_day_54.presentation.hello on macOS and Linux, $env:FLASK_APP = "flask_day_54.presentation.hello" in PowerShell, set FLASK_APP=flask_day_54.presentation.hello in Command Prompt, then flask run).

Lecture 3: the command line. pwd, ls, cd, mkdir, touch and rm (with rm -rf as the command to double-check). flask_day_54.domain.cli_basics lists them with their Windows equivalents: python -m flask_day_54.domain.cli_basics. The screenshot shows the real commands run in a temporary folder.

Lecture 4: __name__ and __main__. A file run directly has __name__ == "__main__"; an imported file has its module name. app.run() sits under that check in hello.py, so there are two ways to start the server: flask --app flask_day_54.presentation.hello run or python -m flask_day_54.presentation.hello. Try python -m flask_day_54.domain.name_demo.

Lecture 5: functions are first-class objects. A function can be passed as an argument (calculate(add, 2, 3)), defined inside another function and returned from it. See flask_day_54.domain.first_class_functions; run it with python -m flask_day_54.domain.first_class_functions.

Lecture 6: decorators and the @ syntax. @make_bold above a function is shorthand for say_hello = make_bold(say_hello). See flask_day_54.domain.decorators; run it with python -m flask_day_54.domain.decorators.

📋 Requirements

Python 3.13 or newer, because the project sets requires-python = ">=3.13" in pyproject.toml.
venv, which is part of Python, to keep the packages in a local .venv.
Flask (the optional web extra) only for the web lectures. The pure-Python lectures need no package.
pytest (the dev extra) to run the tests.
Doxygen, optional, to build the API documentation.

🛠️ Setup

Create and use a local .venv, then upgrade pip and install the project in editable mode.

Windows (PowerShell):

python -m venv .venv
.\.venv\Scripts\Activate.ps1
python -m pip install --upgrade pip
python -m pip install -e ".[dev]"

macOS and Linux:

python3 -m venv .venv
source .venv/bin/activate
python -m pip install --upgrade pip
python -m pip install -e ".[dev]"

Leave the environment with deactivate. The .venv folder is ignored by git. Install only .[web] if you do not need pytest.

▶️ Run

The lecture code is added milestone by milestone. Once the Flask application exists, start the server with either:

flask --app flask_day_54.presentation.hello run
python -m flask_day_54.presentation.hello

Then open http://127.0.0.1:5000/. Stop the server with Ctrl+C.

🧪 Tests

python -m pytest

Optional style checks (the dev extra installs ruff):

python -m ruff format --check src tests
python -m ruff check src tests

📄 License

GNU Affero General Public License v3.0, see LICENSE.

🔗 Links

📎 Appendix: Project documents

Document	What it tells you
AGENTS.md	The rules AI agents follow in this repository
Business Case	Why the project exists, its scope and success criteria
Stakeholder Analysis	Who is involved; the stakeholder IDs used for owners and reviewers
Project Plan	The gateways and their schedule
Milestones	One document per gateway: Go/No-Go criteria and tasks
Artifact registry	Where each artifact type lives, the next version, the PO language and domain
Domain dictionary	The PO terms and the IT terms
Traceability matrix	How the artifacts link and when each was last reviewed
Framework README	The framework this project uses
Framework changelog	What changed in each framework release

Udemy 100 Days of Code, Day 54: Flask basics, the command line, __name__/__main__, first-class functions and decorators. Runnable Python 3.13 code with pytest tests and a wiki in English, Danish and Bahasa Malaysia.

100-days-of-code decorators first-class-functions flask learning pytest python python-bootcamp tutorial udemy

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