Singleton FileChangeAwareCache

Introduction

This class is a singleton class that stores data to file. Also the cache is invalidated when the file is changed. The data can be anything that can be pickled.

It is used to store data that is not sensitive and can be shared between different instances of the same class.

This class is more of a dynamic singleton class. When the same parameter is passed to the constructor, the same instance is returned. If the parameter is different, a new instance is created. Custom key value pairs can be passed to the constructor to create a new instance. Custom key value pairs must be hashable.

New in version 0.52.0.

Examples

This example store data in a the LibreOffice tmp directory. Something like /tmp/ooo_uno_tmpl/my_tmp/x75c002da1ba8f255013111f3084243be.pkl.

The cache is set to expire when file changes.

from __future__ import annotations
from typing import Any
import json
from pathlib import Path
from ooodev.utils.cache.singleton import FileChangeAwareCache

def get_json_data(json_file: str | Path) -> Any:
    with open(json_file, 'r', encoding="utf-8") as json_file:
        data = json.load(json_file)
    return data

def save_json_data(json_file: str | Path, data: Any) -> None:
    with open(json_file, 'w', encoding="utf-8") as json_file:
        json.dump(data, json_file)

def get_cache_data(cache: FileChangeAwareCache, json_file: str | Path) -> Any:
    data = cache[json_file]
    if data is None:
        data = get_json_data(json_file)
        cache[json_file] = data
    return data

cache = FileChangeAwareCache(tmp_dir="my_tmp")
json_file = Path("/user/me/Documents/User.json")

data = get_cache_data(json_file)

data["new_key"] = "new_value"
# once the file is changed, the cache is invalidated
save_json_data(json_file, data)

data = get_cache_data(json_file)
assert data["new_key"] == "new_value"

Class

class ooodev.utils.cache.singleton.FileChangeAwareCache(*, tmp_dir='', **kwargs)[source]

Bases: object

Singleton Class. Caches files and retrieves cached files. Cached file are in ``ooo_uno_tmpl` subdirectory of LibreOffice tmp dir.