Effecton — Python optimized for AI

Harden it, one line at a time

With Effecton33 lines

import effecton as E


class TooLate(E.EffectonError): ...


class Closed(E.EffectonError): ...


@E.gen
def greet(
    name: str,
) -> E.EffectGen[str, TooLate | Closed]:
    now = yield from E.now()
    if now.weekday() == 6:
        yield from E.fail(Closed())
    if now.hour >= 22:
        yield from E.fail(TooLate())
    return f"hello {name}"


program = (
    greet("ada")
    .retry(  # typesafe retries
        E.Schedule.spaced(minutes=1),
        until=lambda e: isinstance(e, Closed),
    )
    .with_span(  # observability built in
        "greet"
    )
)

E.run_main(program)

Add a guarantee

TimeoutRetryTrace

Without Effecton9 lines

import httpx


async def fetch_profile(
    client: httpx.AsyncClient, user_id: int
) -> str:
    response = await client.get(f"/users/{user_id}")
    response.raise_for_status()
    return response.text

With Effecton17 lines

import effecton as E


type FetchError = (
    E.HttpClient.TransportError | E.HttpClient.StatusError
)


@E.gen
def fetch_profile(
    user_id: int,
) -> E.EffectGen[str, FetchError, E.HttpClient.Protocol]:
    http = yield from E.require(E.HttpClient.Protocol)

    response = yield from http.get(f"/users/{user_id}")
    ok = yield from E.HttpClient.filter_status_ok(response)
    return ok.text

E.Effect describes your program

def charge(
    order: Order,
) -> E.Effect[
    Receipt, 
    CardDeclined | CardExpired, 
    PaymentGateway,
]: ...

Success · Receipt

What it produces

The value a successful run hands back. Use, yield from charge(order) and possible errors automatically propagate. Just like with async / await code.

Error · CardDeclined | CardExpired

How it can fail

Every expected failure, as a union of plain classes. Implement granular, type-safe error handling with catch(CardExpired).

Requirements · PaymentGateway

What it needs

The services the program depends on. Inject Live dependencies in your production code and mocks in tests. Type checker knows when you forget to do so.

Agent-era ready Python

Type safe to the limit

Every function says what it returns, how it can fail and what it needs, right in its signature. You and your agent sees the whole interface.

Unsloppable code

Agents love building from reusable building blocks. Small, typed, composable primitives are easy for a model to reason about.

Your agent already knows Effecton

Just point it to the docs. Your agent is already effecton expert.

Building blocks to build whatever you want

Building blocks

HTTP clientsync and async, on httpx
File systemsync and async
In-memory file systemthe Test double
Pretty loggerlevels, colour, annotations
Clocka test clock you can wind
TracerOpenTelemetry spans
Randomseedable in tests
Processcwd and home
Schedulespaced, exponential, jittered

What they add up to

Web APIs

Typed handlers with built-in retries and tracing

Command-line tools

Testable side effects, structured errors

ML pipelines

Reliable steps that retry, time out, and log themselves