Setup the database operations

Here we grab Step 2 and Step 4 from the original article and mostly ignored other code portions.

As we have several helper codes we can store them in the _todos package:

$ tree
.
└── TODO
    ├── init.py
    ├── remove.py
    ├── rename.py
    ├── todo
    └── _todos
        ├── database.py
        └── __init__.py

2 directories, 6 files

Let's add some preliminary constants:

__init__.py

(
    SUCCESS,
    DIR_ERROR,
    FILE_ERROR,
    DB_READ_ERROR,
    DB_WRITE_ERROR,
    JSON_ERROR,
    ID_ERROR,
) = range(7)

ERRORS = {
    DIR_ERROR: "config directory error",
    FILE_ERROR: "config file error",
    DB_READ_ERROR: "database read error",
    DB_WRITE_ERROR: "database write error",
    ID_ERROR: "to-do id error",
}

As you may notice we have removed redundant app name and version information from the __init__.py which was described in Step 2.

Let's add our database handler class:

database.py

import json
from typing import NamedTuple, Any
from . import JSON_ERROR, SUCCESS, DB_READ_ERROR, DB_WRITE_ERROR


class DBResponse(NamedTuple):
    todo_list: dict[str, list[list[str, Any]]]
    error: int


class DatabaseHandler:

    def __init__(self, db_path: str) -> None:
        self._db_path = db_path

    def read_todos(self) -> DBResponse:
        try:
            with open(self._db_path, "r") as db:
                try:
                    return DBResponse(json.loads(db.readline()), SUCCESS)
                except json.JSONDecodeError:  # Catch wrong JSON format
                    return DBResponse({}, JSON_ERROR)
        except OSError:  # Catch file IO problems
            return DBResponse({}, DB_READ_ERROR)

    def write_todos(self, todo_list: dict[str, list[list[str, Any]]]) -> DBResponse:
        try:
            with open(self._db_path, "w") as db:
                json.dump(todo_list, db)
            return DBResponse(todo_list, SUCCESS)
        except OSError:  # Catch file IO problems
            return DBResponse(todo_list, DB_WRITE_ERROR)

Again, we have slightly changed the code but most of it is from Step 4.

We added an extra package to our CLI path, it should be broken right now? Of course not.

In pure Python convention, the names which are started with _(underscore) are considered "non-public". DynaCLI follows this convention, and we just ignore "non-public" packages - they are not considered as part of CLI.

The next is to add a Controller class for our TODOs.