README.md

@@ -37,6 +37,14 @@ Each lecture has its own screenshot in `docs/images/` (made by `docs/images/capt
 
 ![Lecture 2: Hello, World! in the browser](docs/images/lecture-02.png)
 
+**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 3: the command line](docs/images/lecture-03.png)
+
+**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 4: __name__ and __main__](docs/images/lecture-04.png)
+
 ## 📋 Requirements
 
 - Python 3.13 or newer, because the project sets `requires-python = ">=3.13"` in `pyproject.toml`.

docs/artifact-registry.md

@@ -18,7 +18,7 @@ document of a type. `Primary File` may contain a glob (e.g.
 | ADR | Architecture Decision Record | docs/adr/adr-NNNN-*.md | 0002 |
 | DICT | Domain Dictionary | docs/dictionary.md | 002 |
 | TM | Traceability Matrix | docs/sqa/traceability-matrix.md | 002 |
-| RC | SQA Review Record | docs/sqa/reviews/rc-*.md | 017 |
+| RC | SQA Review Record | docs/sqa/reviews/rc-*.md | 018 |
 
 ## Languages
 

docs/images/capture.py

@@ -11,6 +11,7 @@ Usage (from the repository root, with the project's .venv active):
 
 import html
 import os
+import re
 import shutil
 import subprocess
 import sys
@@ -101,6 +102,15 @@ def terminal_page(title: str, entries: list[tuple[str, str]], png: Path, height:
     shot(src, png, 900, height)
 
 
+def stop(proc: subprocess.Popen) -> None:
+    """Stop a server and its reloader child."""
+    if os.name == "nt":
+        subprocess.run(["taskkill", "/F", "/T", "/PID", str(proc.pid)], capture_output=True)  # nosemgrep
+    else:
+        proc.kill()
+    proc.wait(timeout=10)
+
+
 def python() -> str:
     return sys.executable
 
@@ -141,7 +151,7 @@ def step2() -> None:
         src.write_text(page, encoding="utf-8")
         shot(src, OUT / "lecture-02.png", 700, 230)
     finally:
-        proc.kill()
+        stop(proc)
 
 
 def step3() -> None:
@@ -153,11 +163,11 @@ def step3() -> None:
         "ls",
         "mkdir my_project",
         "cd my_project && touch hello.py && ls",
-        "cd .. && rm -rf my_project && ls",
+        "rm -rf my_project && ls",
     ]
     for command in script:
         output = run([bash, "-c", command], work)
-        entries.append((command, output.replace(str(work).replace("\\", "/"), "~/demo")))
+        entries.append((command, re.sub(r"/tmp/cli-demo-\w+", "~/demo", output)))
     shutil.rmtree(work, ignore_errors=True)
     terminal_page("Terminal - lecture 3: the command line", entries, OUT / "lecture-03.png", 330)
 
@@ -188,8 +198,13 @@ def step4() -> None:
         text=True,
     )
     time.sleep(3)  # nosemgrep
-    server.kill()
+    stop(server)
-    out = (server.stdout.read() if server.stdout else "").strip()
+    raw = (server.stdout.read() if server.stdout else "").strip()
+    # Leave out the .env tip and the random debugger PIN; they say nothing about the lecture.
+    kept = [
+        line for line in raw.splitlines() if "Tip:" not in line and "Debugger PIN" not in line
+    ]
+    out = "\n".join(kept)
     entries.append(("python -m flask_day_54.presentation.hello", out + "\n^C"))
     terminal_page("Terminal - lecture 4: __name__ and __main__", entries, OUT / "lecture-04.png", 560)
 

docs/images/sources/lecture-03.html

@@ -0,0 +1,12 @@
+<!doctype html><meta charset='utf-8'><style>
+body{margin:0;background:#1e1e1e;font-family:Consolas,'DejaVu Sans Mono',monospace;color:#d4d4d4}
+.bar{background:#333;color:#ccc;padding:8px 14px;font-size:14px}
+pre{margin:0;padding:16px 18px;font-size:15px;line-height:1.45;white-space:pre-wrap}
+.p{color:#6a9955}.c{color:#9cdcfe}
+</style><div class='bar'>Terminal - lecture 3: the command line</div><pre><span class="p">$</span> <span class="c">pwd</span>
+~/demo
+<span class="p">$</span> <span class="c">ls</span>
+<span class="p">$</span> <span class="c">mkdir my_project</span>
+<span class="p">$</span> <span class="c">cd my_project &amp;&amp; touch hello.py &amp;&amp; ls</span>
+hello.py
+<span class="p">$</span> <span class="c">rm -rf my_project &amp;&amp; ls</span></pre>

docs/images/sources/lecture-04.html

@@ -0,0 +1,18 @@
+<!doctype html><meta charset='utf-8'><style>
+body{margin:0;background:#1e1e1e;font-family:Consolas,'DejaVu Sans Mono',monospace;color:#d4d4d4}
+.bar{background:#333;color:#ccc;padding:8px 14px;font-size:14px}
+pre{margin:0;padding:16px 18px;font-size:15px;line-height:1.45;white-space:pre-wrap}
+.p{color:#6a9955}.c{color:#9cdcfe}
+</style><div class='bar'>Terminal - lecture 4: __name__ and __main__</div><pre><span class="p">$</span> <span class="c">python -m flask_day_54.domain.name_demo</span>
+Running as the main program: the file was executed directly
+<span class="p">$</span> <span class="c">python -c &quot;import flask_day_54.domain.name_demo as m; print(m.describe_name(m.__name__))&quot;</span>
+Running as an imported module named flask_day_54.domain.name_demo
+<span class="p">$</span> <span class="c">python -m flask_day_54.presentation.hello</span>
+ * Serving Flask app &#x27;hello&#x27;
+ * Debug mode: on
+WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
+ * Running on http://127.0.0.1:5000
+Press CTRL+C to quit
+ * Restarting with stat
+ * Debugger is active!
+^C</pre>

docs/sqa/reviews/rc-017-code-mil-003-cli-and-main.md

@@ -0,0 +1,62 @@
+# Review of MIL-003
+
+## Metadata
+| Key | Value |
+| --- | --- |
+| ID | RC-017 |
+| CrossReference | [MIL-003], [QC-PY-001] |
+
+## Version History
+| Date | Status | Author | Reviewer | Change | Commit |
+| --- | --- | --- | --- | --- | --- |
+| 2026-11-06 | Proposed | Jens Tirsvad Nielsen | AI as stand-in for S01 | Initial version | [f8a1794] |
+
+---
+
+## Artifact Under Review
+
+- Instance reviewed: [MIL-003]
+- Checklist used: [QC-PY-001]
+- Scope: full review of the source and tests delivered by MIL-003 (src/, tests/)
+- Language and domain: n/a
+- Language reviewer: none (the reviewer reads English and knows the IT domain)
+- Mode: autonomous, not independent (AI as stand-in for S01)
+
+## Checklist Results
+
+| # | Criterion | Status | Evidence/Notes |
+| --- | --- | --- | --- |
+| 1 | Packages, modules, functions, variables, classes and constants follow PEP 8 casing (`snake_case`, `PascalCase`, `UPPER_SNAKE`) | Pass | Modules, functions and constants use snake_case / UPPER_SNAKE; classes none or PascalCase. |
+| 2 | Names state purpose in the domain's language; no unexplained abbreviations, no single-letter names outside tiny scopes | Pass | Names follow the lecture and the domain dictionary. |
+| 3 | Code is produced by the project's formatter and passes its linter with no unexplained suppressions | Pass | `ruff format` leaves files unchanged and `ruff check` (E, F, I, B, UP) passes; configured in pyproject.toml. |
+| 4 | Every function and method signature is type-annotated, including `-> None` | Pass | Every function signature is annotated, including `-> None`. |
+| 5 | No bare `except:`, no swallowed exceptions; specific exceptions are raised and the cause is kept (`raise ... from`) | Pass | No bare except and no swallowed exception. |
+| 6 | No mutable default arguments and no shadowed builtins | Pass | No mutable defaults; no builtin shadowed. |
+| 7 | Files, locks and connections are managed with context managers | N-A | No file, lock or connection is opened. |
+| 8 | Public modules, classes and functions have docstrings that say what, not how | Pass | Module and public names carry docstrings plus Doxygen comments. |
+| 9 | Logging uses `logging`, not `print`; no secrets or personal data in log output | N-A | Console output of the demo entry points (print under the __main__ guard) is the program's result, not diagnostic logging; no secrets handled. |
+| 10 | Classes and operations trace to the Design Class Diagram they implement; deviations are recorded | N-A | No DCD exists in this project; the layered layout is recorded in ADR-0001. |
+| 11 | Tests exist for new behaviour, are named for the behaviour, and do not depend on order or the network | Pass | pytest tests named for behaviour; no order or network dependence. |
+| 12 | Type checker runs in strict mode without errors; `Any` is justified in a comment | N-A | No type checker is configured (optional criterion). |
+| 13 | Dependencies are declared and pinned in the project's dependency file, none unused | Pass | Dependencies are declared in pyproject.toml; none unused (Flask is the optional `web` extra). |
+| 14 | Each piece of knowledge (a business rule, constant, format, validation or query) is defined in one place; code is merged only where it expresses the same knowledge, not where it merely looks alike | Pass | Each constant is defined once in the constants.py of its layer. |
+| 15 | Imports point inward: business-rule modules import no framework, database, UI or delivery-mechanism code, and there are no import cycles | Pass | `domain` imports no framework or outer layer; imports point inward; no cycles. |
+| 16 | SOLID holds: a class or module has one reason to change; new behaviour is added by extension, not by editing a type test in several places; subclasses honour the contract of their base; protocols are narrow; high-level code depends on protocols or abstract types and receives its implementations | Pass | Small modules with one reason to change; no type tests or subclass hierarchies. |
+| 17 | Source is laid out in the layers and folders of the clean architecture folder structure (`domain`, `application`, `infrastructure`, `presentation` packages under `src/`, and `unit`, `integration` and `e2e` under `tests/`), in `snake_case`, and imports between the layers point inward | Pass | Layers domain, application, infrastructure, presentation under src/flask_day_54; tests in unit and e2e (ADR-0001); no layer merged. |
+| 18 | File and folder names are English, contain no space and no character outside letters, digits, `-`, `_` and `.`, and follow the casing of the language for files | Pass | English snake_case file names without spaces. |
+
+## Overall Verdict
+
+Go — All applicable mandatory criteria pass.
+
+## Action Items
+
+| Action | Owner | Due |
+| --- | --- | --- |
+| None | S01 | - |
+
+---
+
+[MIL-003]: ../../milestones/mil-003-cli-and-main.md
+[QC-PY-001]: ../../../framework/qc/code/qc-programming-python.md
+[f8a1794]: https://git.tirsystem.com/Tirsvad-Udemy-100-days-of-code/054-flask/commit/f8a1794373b21d718d756215eae34c67e873fbd2

src/flask_day_54/domain/cli_basics.py

@@ -0,0 +1,66 @@
+## @file cli_basics.py
+#  @brief Lecture 3 command line cheat sheet.
+"""Command line cheat sheet with Windows equivalents."""
+
+from dataclasses import dataclass
+
+from flask_day_54.domain.constants import CLI_COMMANDS
+
+
+## @brief One command of the cheat sheet.
+@dataclass(frozen=True, slots=True)
+class CommandInfo:
+    """A shell command, its purpose, Windows equivalent and risk."""
+
+    name: str
+    purpose: str
+    windows_equivalent: str
+    is_destructive: bool
+    warning: str
+
+
+def _all_commands() -> tuple[CommandInfo, ...]:
+    return tuple(CommandInfo(*row) for row in CLI_COMMANDS)
+
+
+## @brief Look up one command by name.
+#  @param name Command name such as "ls" or "rm -rf".
+#  @return The command information.
+#  @throws ValueError When the command is not in the cheat sheet.
+def describe_command(name: str) -> CommandInfo:
+    """Return the cheat sheet entry for a command name."""
+    for command in _all_commands():
+        if command.name == name:
+            return command
+    raise ValueError(f"Unknown command: {name!r}")
+
+
+## @brief List the commands that remove data without asking.
+def destructive_commands() -> tuple[CommandInfo, ...]:
+    """Return the destructive commands."""
+    return tuple(c for c in _all_commands() if c.is_destructive)
+
+
+## @brief Format the cheat sheet as text, one command per line.
+def format_cheat_sheet() -> str:
+    """Return the cheat sheet as multi-line text."""
+    lines: list[str] = []
+    for command in _all_commands():
+        line = (
+            f"{command.name:<8} {command.purpose} "
+            f"(Windows: {command.windows_equivalent})"
+        )
+        if command.is_destructive:
+            line += f" WARNING: {command.warning}"
+        lines.append(line)
+    return "\n".join(lines)
+
+
+## @brief Print the cheat sheet.
+def main() -> None:
+    """Print the cheat sheet; the output is the lecture's result."""
+    print(format_cheat_sheet())
+
+
+if __name__ == "__main__":
+    main()

src/flask_day_54/domain/constants.py

@@ -6,3 +6,35 @@ from typing import Final
 
 ## @brief The greeting shown by the first Flask route.
 GREETING: Final[str] = "Hello, World!"
+
+## @brief Value of `__name__` when a file is executed directly.
+MAIN_MODULE_NAME: Final[str] = "__main__"
+
+## @brief Sentence shown when the file runs as the main program.
+MAIN_PROGRAM_SENTENCE: Final[str] = (
+    "Running as the main program: the file was executed directly"
+)
+
+## @brief Sentence template shown when the file is imported; `{name}` is the module.
+IMPORTED_MODULE_SENTENCE: Final[str] = "Running as an imported module named {name}"
+
+## @brief Warning shown for commands that remove data without asking.
+NO_CONFIRMATION_WARNING: Final[str] = "No confirmation is asked - double-check the path"
+
+## @brief Command line cheat sheet rows.
+#  Each row is (name, purpose, Windows equivalent, is destructive, warning).
+CLI_COMMANDS: Final[tuple[tuple[str, str, str, bool, str], ...]] = (
+    ("pwd", "Print the current working directory", "cd", False, ""),
+    ("ls", "List the files in a directory", "dir", False, ""),
+    ("cd", "Change the current directory", "cd", False, ""),
+    ("mkdir", "Create a new directory", "mkdir", False, ""),
+    ("touch", "Create an empty file", "type nul > file", False, ""),
+    ("rm", "Remove a file", "del file", True, NO_CONFIRMATION_WARNING),
+    (
+        "rm -rf",
+        "Remove a directory and everything in it",
+        "rmdir /s /q",
+        True,
+        NO_CONFIRMATION_WARNING,
+    ),
+)

src/flask_day_54/domain/name_demo.py

@@ -0,0 +1,29 @@
+## @file name_demo.py
+#  @brief Lecture 4 demo of the `__name__ == "__main__"` check.
+"""Shows whether a file runs as the main program or as an imported module."""
+
+from flask_day_54.domain.constants import (
+    IMPORTED_MODULE_SENTENCE,
+    MAIN_MODULE_NAME,
+    MAIN_PROGRAM_SENTENCE,
+)
+
+
+## @brief Describe how a module is running from its `__name__`.
+#  @param name The value of `__name__`.
+#  @return A short sentence.
+def describe_name(name: str) -> str:
+    """Return a sentence telling how the module with this name is running."""
+    if name == MAIN_MODULE_NAME:
+        return MAIN_PROGRAM_SENTENCE
+    return IMPORTED_MODULE_SENTENCE.format(name=name)
+
+
+## @brief Print the description of this module's own `__name__`.
+def main() -> None:
+    """Print how this file is running; the output is the demo's result."""
+    print(describe_name(__name__))
+
+
+if __name__ == "__main__":
+    main()

src/flask_day_54/presentation/hello.py

@@ -1,10 +1,11 @@
 ## @file hello.py
-#  @brief The minimal Flask application of lectures 1 and 2.
+#  @brief The minimal Flask application of lectures 1 to 4.
-"""The minimal Flask application of lectures 1 and 2."""
+"""The minimal Flask application of lectures 1 to 4."""
 
 from flask import Flask
 
 from flask_day_54.application.get_greeting import get_greeting
+from flask_day_54.infrastructure.constants import DEBUG, HOST, PORT
 
 ## @brief The Flask application object.
 app = Flask(__name__)
@@ -16,3 +17,13 @@ app = Flask(__name__)
 def hello_world() -> str:
     """Answer the root route with the greeting."""
     return get_greeting()
+
+
+## @brief Start the Flask development server with the configured settings.
+def main() -> None:
+    """Run the development server using the infrastructure settings."""
+    app.run(host=HOST, port=PORT, debug=DEBUG)
+
+
+if __name__ == "__main__":
+    main()

tests/e2e/test_hello_main.py

@@ -0,0 +1,33 @@
+import importlib
+
+import pytest
+
+flask = pytest.importorskip("flask")
+
+from flask_day_54.infrastructure.constants import DEBUG, HOST, PORT  # noqa: E402
+
+
+def test_main_runs_app_with_configured_host_port_and_debug(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    from flask_day_54.presentation import hello
+
+    calls: list[dict[str, object]] = []
+    monkeypatch.setattr(hello.app, "run", lambda **kwargs: calls.append(kwargs))
+
+    hello.main()
+
+    assert calls == [{"host": HOST, "port": PORT, "debug": DEBUG}]
+
+
+def test_importing_module_does_not_start_server(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    from flask_day_54.presentation import hello
+
+    calls: list[object] = []
+    monkeypatch.setattr(flask.Flask, "run", lambda *args, **kwargs: calls.append(args))
+
+    importlib.reload(hello)
+
+    assert calls == []

tests/unit/test_cli_basics.py

@@ -0,0 +1,39 @@
+import pytest
+
+from flask_day_54.domain.cli_basics import (
+    describe_command,
+    destructive_commands,
+    format_cheat_sheet,
+)
+
+
+def test_describe_command_returns_windows_equivalent_when_known() -> None:
+    assert describe_command("ls").windows_equivalent == "dir"
+    assert describe_command("touch").windows_equivalent == "type nul > file"
+    assert describe_command("pwd").windows_equivalent == "cd"
+
+
+def test_describe_command_raises_value_error_when_unknown() -> None:
+    with pytest.raises(ValueError, match="Unknown command: 'foo'"):
+        describe_command("foo")
+
+
+def test_destructive_commands_contains_only_rm_variants() -> None:
+    names = {c.name for c in destructive_commands()}
+
+    assert names == {"rm", "rm -rf"}
+
+
+def test_recursive_remove_has_warning_and_windows_equivalent() -> None:
+    command = describe_command("rm -rf")
+
+    assert command.windows_equivalent == "rmdir /s /q"
+    assert command.warning == "No confirmation is asked - double-check the path"
+
+
+def test_format_cheat_sheet_lists_every_command_and_warns_on_rm() -> None:
+    text = format_cheat_sheet()
+
+    for name in ("pwd", "ls", "cd", "mkdir", "touch", "rm", "rm -rf"):
+        assert name in text
+    assert text.count("WARNING") == 2

tests/unit/test_name_demo.py

@@ -0,0 +1,17 @@
+from flask_day_54.domain.name_demo import describe_name
+
+
+def test_describe_name_reports_main_program_when_name_is_main() -> None:
+    assert describe_name("__main__") == (
+        "Running as the main program: the file was executed directly"
+    )
+
+
+def test_describe_name_reports_imported_module_when_name_is_other() -> None:
+    assert describe_name("flask_day_54.domain.name_demo") == (
+        "Running as an imported module named flask_day_54.domain.name_demo"
+    )
+
+
+def test_describe_name_reports_imported_module_when_name_is_empty() -> None:
+    assert describe_name("") == "Running as an imported module named "