quadkit-contracts

Protocols, shared types, and the exception hierarchy for Quadkit — with zero runtime dependencies beyond typing-extensions. Every published package depends on contracts; no implementation package defines a protocol another package depends on.

For integration authors who need to bind against Quadkit interfaces without pulling in the framework — thin adapters import only this package.

The quadkit family

Installation

uv add quadkit-contracts

Requires Python >= 3.11.

Minimal working example

Protocols are structural: implement the shape, and the container binds your implementation to the contract.

from typing import Protocol

from quadkit.result import Err, Ok, Result


class UserNotFound(Exception):
    """A domain failure the caller is expected to handle."""


class UserRepository(Protocol):
    async def find_name(self, user_id: str) -> Result[str, UserNotFound]: ...


async def find_name_or_unknown(repo: UserRepository, user_id: str) -> str:
    result = await repo.find_name(user_id)
    return result.match(ok=lambda name: name, err=lambda e: "unknown")

The domain-model side — pydantic-based entities and events:

from quadkit.contracts.domain.events import DomainEvent
from quadkit.domain import AggregateRoot


class UserCreated(DomainEvent):
    user_id: str
    email: str


class User(AggregateRoot):
    email: str

The Result toolkit

Result is this package's flagship: expected failures become values the type system can see. pipeline() chains fallible steps fluently; as_result wraps exception-raising calls without swallowing the unexpected ones:

from quadkit.result import Err, Ok, as_result, pipeline


def parse_port(raw: str):
    try:
        port = int(raw)
    except ValueError as exc:
        return Err(exc)
    if not 1 <= port <= 65535:
        return Err(ValueError(f"port out of range: {port}"))
    return Ok(port)


result = (
    pipeline("8080")  # infallible start
    .then(parse_port)  # Result[int, ValueError]
    .map(lambda port: f"listening on :{port}")
    .finalize()  # Result[str, ValueError]
)


@as_result(ValueError, TypeError)  # only these become Err
async def load_setting(raw: str) -> int:
    return int(raw)

collect() gathers many results, partition() splits them into successes and failures, and try_catch() is the sync counterpart of as_result. Full walkthrough: contracts — errors as values.

Optional extras

Public API entry points

Deep-dive: contracts in the docs set.

Configuration

None — this package carries types, not behavior.

Error handling

The taxonomy lives here: QuadkitError is the root; DomainError subclasses describe expected business failures (NotFoundError, ValidationError, ConflictError, PermissionDeniedError, ...). The web layer maps them to HTTP problem responses — see error handling.

Testing

Protocols are tested by conformance: implement the shape, run your implementation through the behavior callers rely on. quadkit-testing ships the fakes used by the framework's own tests.

Security

This package ships interfaces and types only — no network, no I/O, no runtime dependencies. Report vulnerabilities privately per SECURITY.md.

Stability

Version 0.0.3 in the 0.x series, released in lockstep with the other four distributions. These protocols carry no compatibility guarantee yet: minor releases may add, rename, or remove members while the framework is pre-1.0. Because this package is published whole, protocols for not-yet-released areas are the most likely to change; the settled ones are those exercised by quadkit, quadkit-web, quadkit-testing, and quadkit-cli. Pin an exact version (quadkit-contracts==0.0.3) when you depend on these types directly. Full policy: stability and compatibility.

Links

• Documentation — https://dbtinoy-.github.io/quadkit/
• Getting started — https://dbtinoy-.github.io/quadkit/getting-started/installation/
• Changelog — https://github.com/dbtinoy-/quadkit/blob/main/CHANGELOG.md
• Issues — https://github.com/dbtinoy-/quadkit/issues
• Security — report privately per SECURITY.md
• Contributing — CONTRIBUTING.md

Apache-2.0 — see LICENSE. "Quadkit" and the Quadkit logo are trademarks of the project — see TRADEMARK.md.