2.3.5 Follow-Along Workshop: Build a Local Learning Task Assistant

Workshop goal

This page is the practical bridge for Chapter 2. You will not just read syntax explanations; you will build a small tool that can create learning tasks, save them to JSON, mark tasks as done, show statistics, and export a Markdown report.

What you will build

You will build a command-line learning task assistant named learning_assistant_cli.py. It uses only the Python standard library, so you do not need to install third-party packages.

After following the steps, you will be able to run commands like:

python3 learning_assistant_cli.py seed
python3 learning_assistant_cli.py list
python3 learning_assistant_cli.py add "Practice command-line arguments" --stage 2.3 --tag argparse
python3 learning_assistant_cli.py done 2
python3 learning_assistant_cli.py stats
python3 learning_assistant_cli.py export

The project will create:

File	Purpose
learning_assistant_cli.py	The runnable Python program
ch02_output/tasks.json	Saved learning tasks
ch02_output/learning_report.md	Exported portfolio evidence

Step 0: Create a clean practice folder

Run these commands in a terminal:

mkdir ch02-learning-assistant-workshop
cd ch02-learning-assistant-workshop
python3 --version

Expected output looks like this. The exact version number can be different.

Python 3.12.3

This workshop uses modern Python standard-library features such as dataclass, list[str], and str | None. Use Python 3.10 or newer.

Step 1: See the whole program before typing

The program follows one simple route:

Step	What happens	Python concept
User types a command	add, list, done, stats, or export	command-line arguments
argparse parses it	The command becomes structured data	functions and modules
The program loads JSON	Existing tasks are read from disk	file I/O and exceptions
A command function runs	Data is changed or summarized	lists, dictionaries, loops
The program saves output	JSON or Markdown is written back	persistence

Keep this picture in mind while reading the code. You are building a small but complete program, not just practicing isolated syntax.

Step 2: Create the full script

Create a file named learning_assistant_cli.py, then paste the code below.

from __future__ import annotations

import argparse
import json
from dataclasses import asdict, dataclass, field
from datetime import datetime, timezone
from pathlib import Path

OUTPUT_DIR = Path("ch02_output")
DATA_FILE = OUTPUT_DIR / "tasks.json"
REPORT_FILE = OUTPUT_DIR / "learning_report.md"


def utc_now() -> str:
    return datetime.now(timezone.utc).replace(microsecond=0).isoformat()


@dataclass
class Task:
    id: int
    title: str
    stage: str
    tags: list[str]
    done: bool = False
    created_at: str = field(default_factory=utc_now)
    completed_at: str | None = None


def ensure_output_dir() -> None:
    OUTPUT_DIR.mkdir(exist_ok=True)


def load_tasks() -> list[Task]:
    if not DATA_FILE.exists():
        return []
    try:
        raw_tasks = json.loads(DATA_FILE.read_text(encoding="utf-8"))
    except json.JSONDecodeError as exc:
        raise SystemExit(f"Cannot read {DATA_FILE}: invalid JSON at line {exc.lineno}. Fix or remove the file, then rerun.") from exc
    return [Task(**item) for item in raw_tasks]


def save_tasks(tasks: list[Task]) -> None:
    ensure_output_dir()
    data = [asdict(task) for task in tasks]
    DATA_FILE.write_text(json.dumps(data, ensure_ascii=False, indent=2), encoding="utf-8")


def next_id(tasks: list[Task]) -> int:
    if not tasks:
        return 1
    return max(task.id for task in tasks) + 1


def seed_tasks(_: argparse.Namespace) -> None:
    tasks = [
        Task(id=1, title="Read Python functions", stage="2.1", tags=["functions"]),
        Task(id=2, title="Practice JSON file saving", stage="2.2", tags=["json", "file-io"]),
        Task(id=3, title="Build the first CLI command", stage="2.3", tags=["cli"]),
    ]
    save_tasks(tasks)
    print(f"Wrote {len(tasks)} sample tasks to {DATA_FILE}")


def add_task(args: argparse.Namespace) -> None:
    title = args.title.strip()
    if not title:
        raise SystemExit("Task title cannot be empty.")
    tasks = load_tasks()
    task = Task(id=next_id(tasks), title=title, stage=args.stage, tags=args.tag)
    tasks.append(task)
    save_tasks(tasks)
    print(f"Added task #{task.id}: {task.title}")


def list_tasks(_: argparse.Namespace) -> None:
    tasks = load_tasks()
    if not tasks:
        print("No tasks yet. Run: python learning_assistant_cli.py add \"Read functions\"")
        return
    print("ID  Status  Stage  Title")
    print("--  ------  -----  -----")
    for task in tasks:
        status = "done" if task.done else "todo"
        print(f"{task.id:<2}  {status:<6}  {task.stage:<5}  {task.title}")


def complete_task(args: argparse.Namespace) -> None:
    tasks = load_tasks()
    for task in tasks:
        if task.id == args.id:
            task.done = True
            task.completed_at = utc_now()
            save_tasks(tasks)
            print(f"Completed task #{task.id}: {task.title}")
            return
    raise SystemExit(f"Task #{args.id} was not found.")


def show_stats(_: argparse.Namespace) -> None:
    tasks = load_tasks()
    total = len(tasks)
    done = sum(task.done for task in tasks)
    todo = total - done
    by_stage: dict[str, int] = {}
    for task in tasks:
        by_stage[task.stage] = by_stage.get(task.stage, 0) + 1
    rate = (done / total * 100) if total else 0
    print(f"Total tasks: {total}")
    print(f"Done: {done}")
    print(f"Todo: {todo}")
    print(f"Completion rate: {rate:.1f}%")
    print("Tasks by stage:")
    for stage, count in sorted(by_stage.items()):
        print(f"- {stage}: {count}")


def export_report(_: argparse.Namespace) -> None:
    tasks = load_tasks()
    done = sum(task.done for task in tasks)
    total = len(tasks)
    lines = [
        "# Python Learning Assistant Report",
        "",
        f"Generated at: {utc_now()}",
        f"Total tasks: {total}",
        f"Completed tasks: {done}",
        "",
        "## Tasks",
        "",
    ]
    for task in tasks:
        checkbox = "x" if task.done else " "
        tags = ", ".join(task.tags) if task.tags else "-"
        lines.append(f"- [{checkbox}] #{task.id} {task.title} (stage {task.stage}; tags: {tags})")
    ensure_output_dir()
    REPORT_FILE.write_text("\n".join(lines) + "\n", encoding="utf-8")
    print(f"Exported report to {REPORT_FILE}")


def build_parser() -> argparse.ArgumentParser:
    parser = argparse.ArgumentParser(description="Local learning-task assistant for Chapter 2 Python practice.")
    subparsers = parser.add_subparsers(dest="command", required=True)

    seed_parser = subparsers.add_parser("seed", help="Create sample tasks.")
    seed_parser.set_defaults(func=seed_tasks)

    add_parser = subparsers.add_parser("add", help="Add one learning task.")
    add_parser.add_argument("title", help="Task title, wrapped in quotes if it contains spaces.")
    add_parser.add_argument("--stage", default="2.1", help="Course stage or section, such as 2.1 or 2.3.")
    add_parser.add_argument("--tag", action="append", default=[], help="Repeatable tag, such as --tag functions --tag json.")
    add_parser.set_defaults(func=add_task)

    list_parser = subparsers.add_parser("list", help="List tasks.")
    list_parser.set_defaults(func=list_tasks)

    done_parser = subparsers.add_parser("done", help="Mark one task as complete.")
    done_parser.add_argument("id", type=int, help="Task id to complete.")
    done_parser.set_defaults(func=complete_task)

    stats_parser = subparsers.add_parser("stats", help="Show task statistics.")
    stats_parser.set_defaults(func=show_stats)

    export_parser = subparsers.add_parser("export", help="Export a Markdown report.")
    export_parser.set_defaults(func=export_report)
    return parser


def main() -> None:
    parser = build_parser()
    args = parser.parse_args()
    args.func(args)


if __name__ == "__main__":
    main()

Step 3: Run the first command

python3 learning_assistant_cli.py seed

Expected output:

Wrote 3 sample tasks to ch02_output/tasks.json

Now list the tasks:

python3 learning_assistant_cli.py list

Expected output:

ID  Status  Stage  Title
--  ------  -----  -----
1   todo    2.1    Read Python functions
2   todo    2.2    Practice JSON file saving
3   todo    2.3    Build the first CLI command

Step 4: Add and complete a task

Add a new task:

python3 learning_assistant_cli.py add "Practice command-line arguments" --stage 2.3 --tag argparse

Expected output:

Added task #4: Practice command-line arguments

Mark task 2 as complete:

python3 learning_assistant_cli.py done 2

Expected output:

Completed task #2: Practice JSON file saving

At this point, open ch02_output/tasks.json. You should see normal JSON data. The exact timestamps will be different, but the done field for task 2 should be true.

Step 5: Show statistics and export a report

python3 learning_assistant_cli.py stats

Expected output:

Total tasks: 4
Done: 1
Todo: 3
Completion rate: 25.0%
Tasks by stage:
- 2.1: 1
- 2.2: 1
- 2.3: 2

Export a Markdown report:

python3 learning_assistant_cli.py export

Expected output:

Exported report to ch02_output/learning_report.md

You now have a runnable project and a small report that can be used as portfolio evidence.

Step 6: Understand the important parts

Code piece	What it teaches	Why it matters later
argparse	Convert terminal commands into structured values	Every CLI, script, and automation tool needs clear inputs
@dataclass	Describe one task with fields	Later API models, database rows, and config objects use the same idea
load_tasks()	Read saved JSON and handle bad JSON	Real programs must survive missing or broken files
save_tasks()	Convert Python objects into JSON	This is the minimum version of persistence
command functions	Keep each command in one function	Larger projects rely on clear function boundaries
export_report()	Turn internal data into user-facing output	AI and data tools often need reports, logs, and evidence

Common mistakes and fixes

Problem	Likely cause	Fix
python3: command not found	Your system uses python instead of python3	Try python --version, then run python learning_assistant_cli.py seed
Task #99 was not found.	You tried to complete a task id that does not exist	Run python3 learning_assistant_cli.py list first
invalid JSON error	tasks.json was edited manually and broken	Fix the JSON file or delete it and run seed again
The report is empty	No tasks were created yet	Run seed or add before export
You understand the code but cannot modify it	The whole script feels too large	Change only one command at a time, then rerun the matching command

Mini exercises

1. Add a delete command that removes a task by id.
2. Add a search command that finds tasks containing a keyword.
3. Add a --tag filter to list.
4. Change export_report() to include unfinished tasks first.
5. Deliberately break tasks.json, run list, then write down the error message and your fix.

Portfolio evidence checklist

Keep these files as evidence:

• learning_assistant_cli.py
• ch02_output/tasks.json
• ch02_output/learning_report.md
• A screenshot or copied terminal output showing seed, list, done, stats, and export
• A short README.md explaining how to run the tool and what errors you handled

This is the core habit of Chapter 2: do not stop at syntax. Turn syntax into a small tool that runs, saves data, handles errors, and can be explained.