RemoteState - Python Library

remotestate is the Python runtime for RemoteState apps. It owns the state store, service methods, and server that expose Python state to React.

If you want the high-level product overview, start with the repository root README: RemoteState

Install

pip install remotestate

Or with pixi:

pixi add remotestate

Development

• Python >= 3.12
• from the package directory: cd remotestate-py
• install dependencies with pixi install
• format with pixi run format
• run checks with pixi run checks
• run tests with pixi run tests
• build a wheel with pixi run build

Quick Start

import remotestate as rs


class CounterService(rs.Service):
    def __init__(self) -> None:
        super().__init__(rs.Store({"count": 0, "user": {"name": "forman"}}))

    @rs.action
    async def increment(self) -> None:
        self.store.set("count", self.store.get("count") + 1)

    @rs.query
    async def compute(self, x: float) -> float:
        self.notify(name="Computing", detail="reading current count", progress=50)
        return x * self.store.get("count")


rs.serve(CounterService(), ui_dist="my-ui/dist")

API Overview

The public Python API is exported from remotestate:

• Store and StoreAt
• Service and ServeResult
• action and query
• serve
• path

Store and StoreAt

Store(initial, *, default_factory=None) holds the Python-side application state.

• the root state may be any JSON-serializable value, including a mapping, list, scalar, Pydantic model, or dataclass

• nested dicts, lists, Pydantic models, and dataclasses are all supported

• default_factory receives the missing prefix as a rs.path.Path tuple

• state returns the current root state value

• get(path=(), require=False) reads a value from a path such as ``, user.name, `[0].label`, or `items[0].label`; omit `path` to read the root state value

• set(path, value) writes a value and notifies subscribers

• store[path] and store[path] = value are notebook-friendly aliases for get() and set()

• store.at returns a notebook-friendly accessor of type StoreAt for nested state variables using item or attribute syntax

• store.at.some.path = value for example executes nested set() calls; use item syntax for arrays or keys that are not valid identifiers

• subscribe(callback) receives batched path-to-value updates after changes flush

• default_factory can materialize missing parents while setting nested values

import remotestate as rs


class User:
    def __init__(self, name: str = "", city: str = "") -> None:
        self.name = name
        self.city = city


def defaults(path: rs.path.Path):
    if path == ("user",):
        return User()
    if path == ("items",):
        return []
    return {}


store = rs.Store({}, default_factory=defaults)
store.set("user.city", "Hamburg")
store.set("items[0].label", "foo")
store["items", 0, "label"] = "bar"
store.at.user.city = "Berlin"
store.at.items[0].label = "baz"

assert store.get("user.city") == "Berlin"
assert store.get() is store.state
assert store["items"] == [{"label": "baz"}]
assert store[()] is store.state

get() never calls the default factory. Reads stay side-effect free, and missing values return None unless require=True is passed.

Actions and Queries

Use @action for state-changing service methods and @query for read-only methods.

• @action batches store.set() calls and flushes them as one action_result message.
• @query is read-only; mutating the store inside a query raises PermissionError
• sync and async methods are both supported

class Counter(rs.Service):
    def __init__(self) -> None:
        super().__init__(rs.Store({"count": 0}))

    @rs.action
    def increment(self) -> None:
        self.store.set("count", self.store.get("count") + 1)

    @rs.query
    async def multiply(self, x: float) -> float:
        self.notify(name="Working", progress=25)
        return x * self.store.get("count")

Service Helpers

Service exposes the store and progress helper used by actions and queries:

• notify(name=None, detail=None, progress=None) emits update_task progress messages for tracked calls

The reserved service method name is notify. Store reads and writes use service.store.get(...) and service.store.set(...); get and set remain available for custom actions or queries.

Service._init_app(app) can be overridden to customize the FastAPI app when serve() creates one.

Serving

serve(service, *, ui_dist, mounts, app, cors_origins, display, width, height, host, port, **uvicorn_settings) starts the RemoteState server and connects it to a frontend bundle.

• service is a Service instance
• ui_dist can be a local React build directory or an HTTP(S) URL
• mounts adds additional static paths
• app lets you supply your own FastAPI app
• cors_origins optionally allows browser HTTP requests from specified origins; cross-origin HTTP access is disabled by default
• display controls how the UI is shown: "auto", "browser", "notebook", "none", or a callback
• host and port configure the backend server

By default, RemoteState chooses a free port, opens a browser outside notebooks, and renders inline inside notebooks. Re-running the same notebook cell restarts the server automatically.

serve() returns a ServeResult with the resolved URLs and server handles:

result = rs.serve(CounterService(), ui_dist="my-ui/dist", display="none")

print("Server URL:    ", result.server_url)
print("WebSocket URL: ", result.ws_url)
print("UI Base URL:   ", result.ui_base_url)

Cross-origin access

When the frontend is hosted on a different origin, explicitly allow that origin:

rs.serve(
    CounterService(),
    ui_dist="https://ui.example.com",
    cors_origins=["https://ui.example.com"],
)

Only list origins you trust. cors_origins enables all HTTP methods and request headers for the listed origins, while leaving CORS disabled for every other origin.

Paths

remotestate.path exposes the parsed path types used by Store.default_factory and other advanced integrations. Parsed paths are tuples of string property names and integer array indices, matching the TypeScript package's string | number path segments:

• Path
• PathSegment
• PathInput
• PathSegmentInput

RemoteState paths use a simplified JSONPath subset without the "$." prefix:

• the empty string addresses the root state value
• the first segment may be an identifier, bracketed integer index, or bracketed JSON string key
• later segments may be dotted identifiers, bracketed integer indices, or bracketed JSON string keys
• bracketed string keys may use either single or double quotes; canonical output uses double quotes
• the whole string must match the grammar; prefix parsing is not allowed

Use normalize_path() when accepting raw path inputs, and use parse_path() and format_path() when you need to inspect, validate, or construct string paths.

More Docs

• Repository root README
• TypeScript package README