Core logic explanation

This page contains the business logic for the Todo CLI application.
All core operations like adding, listing, marking, and clearing tasks are defined here.

Storage

Tasks are stored in a file: todo_data.json
The format is JSON, with a list of objects:

JSON

[
  {
    "id": 1,
    "text": "Buy milk",
    "done": false,
    "priority": "medium",
    "created": "2025-06-01T10:00:00+00:00",
    "due": "2025-06-10",
    "tags": ["shopping", "errands"]
  }
]

Task structure

Each task is defined using a TypedDict for type safety and readability:

Python

class TaskDict(TypedDict):
  id: int
  text: str
  done: bool
  priority: Literal["low", "medium", "high"]
  created: str
  due: Optional[str]
  tags: Optional[list[str]]

The default priority for new tasks is “medium”.
The created field is always generated automatically.
The due field is optional and can be left blank.

Function summary

Function	Description
`load_tasks()`	Load tasks from the JSON file
`save_tasks(tasks)`	Save tasks to the JSON file
`add_task(text)`	Add a new task with optional priority and due date
`list_tasks()`	Return all existing tasks
`complete_task(id)`	Mark a task as completed by ID
`delete_task(id)`	Delete a task by ID
`edit_task(...)`	Edit an existing task’s text, priority, due date or tags
`clear_tasks()`	Remove all tasks from the list

File organization

To make the code more maintainable, functions in core.py are grouped by responsibility.

Section	Responsibility	Functions
🔄 File operations	Load and save task data in JSON format	`load_tasks`, `save_tasks`
➕ Task creation	Add new tasks with automatic ID and status	`add_task`
📄 Task reading	Read and return task data	`list_tasks`
✅ Task updates	Modify the status of tasks	`complete_task`
✅ Task edit	Modify the status or content of tasks	`complete_task`, `edit_task`
❌ Task deletion	Remove tasks individually or all at once	`delete_task`, `clear_tasks`

Notes

Task IDs are incremented automatically.
If the storage file is missing or invalid, an empty list is returned.
All tasks are stored in JSON with indent=2 and ensure_ascii=False.
The design is modular and easy to extend to:
- Tags or categories
- Date reminders or recurring tasks
- Database or cloud backends

Get Started

Development

Core logic explanation

Storage

Task structure

Function summary

File organization

Notes

​Storage

​Task structure

​Function summary

​File organization

​Notes

Storage

Task structure

Function summary

File organization

Notes