nestio

Async local storage for Python. One interface, multiple file formats.

Stop writing the same boilerplate every time you need local storage.

nestio provides a consistent async API for JSON, TOML, YAML, TOON, and MessagePack — plus a typed .env loader — with:

• Dot-path access — "user.settings.theme"
• Atomic writes — never leave files half-written
• Automatic locking — safe concurrent writes out of the box
• One API across every supported format

Supported formats: JSON • TOML • YAML • TOON • MessagePack

Same API. Same code. Different format.

Why nestio?

Without nestio:

import json

with open("config.json", "r") as f:
    data = json.load(f)

data["user"]["settings"]["theme"] = "dark"

with open("config.json", "w") as f:
    json.dump(data, f, indent=4)

With nestio:

from nestio.files import JSON

db = JSON("config.json")
await db.set("user.settings.theme", "dark")

Same logic. Less boilerplate.

Installation

pip install nestio

Features

Supported formats

Quickstart

File storage

import asyncio
from nestio.files import JSON  # swap for TOML, YAML, TOON, or MSGPACK — API is identical

async def main():
    db = JSON("data/config.json")

    await db.set("user.name", "Alice")
    await db.set("user.settings.theme", "dark")
    await db.set("user.scores", [])

    name  = await db.get("user.name")            # "Alice"
    theme = await db.get("user.settings.theme")  # "dark"

    await db.append("user.scores", 42)
    await db.update("user.settings", {"language": "en"})
    await db.delete("user.settings.theme")

asyncio.run(main())

TOML

from nestio.files import TOML

cfg = TOML("data/config.toml")
await cfg.set("server.host", "localhost")
await cfg.set("server.port", 8080)
await cfg.update("server", {"debug": True})

YAML

from nestio.files import YAML

cfg = YAML("data/config.yaml")
await cfg.set("server.host", "localhost")
await cfg.set("tags", ["web", "api"])
await cfg.append("tags", "async")

MessagePack

from nestio.files import MSGPACK

cache = MSGPACK("data/cache.msgpack")
await cache.set("session.user_id", 1234)
await cache.set("session.permissions", ["read", "write"])
await cache.append("session.permissions", "admin")

TOON

from nestio.files import TOON

store = TOON("data/context.toon")
await store.set("context.task", "Our favorite hikes")
await store.set("friends", ["ana", "luis", "sam"])
await store.update("context", {"season": "spring_2025"})

Environment variables

nestio.env gives you a typed wrapper around your .env file — no more scattered os.getenv() calls.

from nestio.env import Env

env = Env(".env")  # raises FileNotFoundError if missing

# Basic access
debug = env.get("DEBUG", default="false")
host  = env["HOST"]          # same as os.getenv("HOST")

# Typed getters
port    = env.get_int("PORT")        # int
ratio   = env.get_float("RATIO")     # float
verbose = env.get_bool("VERBOSE")    # True for "true", "1", "yes", "y", "t"
tags    = env.get_list("TAGS")       # splits on "," by default
tags    = env.get_list("TAGS", sep=" ")  # custom separator

# Required variables — raises KeyError if missing or empty
secret  = env.require("SECRET_KEY")

Given a .env file like:

HOST=localhost
PORT=8080
DEBUG=true
TAGS=web,api,async
SECRET_KEY=supersecret

File storage API

All five methods work the same across every format. All are async and must be awaited.

Import from the submodule or the top level — both work:

from nestio.files import JSON   # explicit
from nestio import JSON         # shortcut

get(path, default=None)

Returns the value at the dot-path, or default if it doesn't exist.

value = await db.get("server.host", default="localhost")

set(path, value)

Sets the value at the dot-path. Creates intermediate dicts as needed.

await db.set("server.port", 8080)

delete(path)

Removes the key at the dot-path. Does nothing if the key doesn't exist.

await db.delete("server.port")

append(path, value)

Appends a value to a list at the dot-path. Creates the list if it doesn't exist yet.

await db.append("logs", {"level": "info", "msg": "started"})

update(path, new_data)

Deep-merges a dict into the value at the dot-path. Existing keys not in new_data are preserved.

await db.update("config", {"retries": 3, "timeout": 30})

How it works

• Dot-path access — keys like "a.b.c" resolve through nested dicts automatically.
• Atomic writes — every save writes to a temp file first, then uses os.replace() to swap it in. Your file is never half-written.
• Per-key locking — concurrent writes to the same path are serialized with asyncio.Lock, while independent paths write in parallel. Locks clean up automatically after a TTL.

Format-specific notes

TOON

TOON (Token-Oriented Object Notation) is a compact, human-readable format designed for LLM input. It combines YAML-style indentation for nested objects with CSV-style rows for uniform arrays — achieving up to 40% fewer tokens than JSON while maintaining full round-trip fidelity.

A .toon file produced by nestio looks like this:

context:
  task: Our favorite hikes
  season: spring_2025
friends[3]: ana,luis,sam
hikes[3]{id,name,distanceKm,wasSunny}:
  1,Blue Lake Trail,7.5,true
  2,Ridge Overlook,9.2,false
  3,Wildflower Loop,5.1,true

MessagePack

MessagePack is a binary format — files are not human-readable, but they're smaller and faster to parse than any text-based format. Best for local caches and high-frequency storage where you don't need to inspect files manually.

Roadmap

• JSON support
• TOML support
• YAML support
• MessagePack support
• TOON support
• Atomic writes
• Async locking
• .env loader
• Benchmarks
• Automatic format detection
• More examples

Why I built nestio

I found myself repeatedly writing the same file handling code in async projects:

• Load a file
• Navigate nested dictionaries
• Modify values
• Save safely
• Handle concurrent writes

nestio was created to remove that boilerplate and provide a consistent interface across multiple storage formats.

Requirements

• Python 3.9+
• aiofiles
• pyyaml (YAML)
• tomli (TOML, Python < 3.11 only)
• tomli-w (TOML)
• toons (TOON)
• msgpack (MessagePack)
• python-dotenv (.env loader)

License

MIT © MrBaconHat