unihttp-openapi-generator

Turn an OpenAPI spec into a typed Python API client built on unihttp.

Point it at a spec; get back an installable package with data models, request classes, a sync and/or async client, an exception hierarchy, and authentication wiring. The output is formatted with ruff and type-checks clean under mypy --strict.

Why

• Actually typed. Models, parameters, and return values carry real annotations; the generated code passes mypy --strict. Your editor knows the shape of every request and response.
• Three model backends. Choose adaptix (default), pydantic, or msgspec for the generated models — same client, your serializer.
• Sync, async, or both. Backed by httpx, aiohttp, requests, niquests, or zapros, chosen per client.
• Faithful to the spec. allOf/oneOf/anyOf, discriminated unions, enums, formats, nullable, defaults, multipart uploads, query array styles, security schemes, and error responses are all carried through.
• Proven on large specs. The Stripe, GitHub, OpenAI, and Kubernetes specs each generate clean, importable code that passes ruff and mypy --strict on every serializer.
• Readable, regenerable output. Deterministic, ruff-formatted, organized by tag.

Install

pip install unihttp-openapi-generator
# or, with uv:
uv tool install unihttp-openapi-generator

Quick start

unihttp-openapi-generator generate openapi.yaml \
  --output-dir ./out --package-name acme_client

The spec can be a local path or a URL, in JSON or YAML. Install the result and use it:

pip install ./out

from acme_client import AcmeClient

with AcmeClient(base_url="https://api.example.com", token="...") as client:
    pet = client.pets.get_pet(pet_id=1)   # -> a typed model
    print(pet.name)

What you get

out/
├── pyproject.toml          # installable; pins unihttp + your serializer + backend
├── README.md
└── acme_client/
    ├── __init__.py         # exports the client(s), DEFAULT_BASE_URL, SERVERS
    ├── py.typed
    ├── models.py           # dataclass / BaseModel / msgspec.Struct
    ├── _serialization.py    # request/response (de)serialization wiring
    ├── exceptions.py       # ApiError hierarchy + status -> exception map
    ├── auth.py             # credential middlewares (when the spec defines security)
    ├── methods/<tag>.py    # one request class per operation
    └── client.py           # the client(s)

A request class and the client constructor (real output):

@dataclass
class GetBooking(BaseMethod[GetBookingResponse]):
    """Get a booking

    Returns the details of a specific booking.
    """
    __url__ = "/bookings/{bookingId}"
    __method__ = "GET"

    booking_id: Path[UUID]


class TrainTravelAPIClient(RequestsSyncClient):
    def __init__(self, base_url: str = DEFAULT_BASE_URL, *,
                 session: Any = None, middleware: list[Any] | None = None,
                 token: str | None = None) -> None:
        ...

Using the client

Clients are context managers and close their transport on exit.

from acme_client import AcmeClient

with AcmeClient(base_url="https://api.example.com", token="secret") as client:
    booking = client.bookings.get_booking(booking_id=some_uuid)   # grouped layout
    # client.get_booking(...)   # flat layout

Async clients expose the same surface; their methods are awaitables:

import asyncio
from acme_client import AsyncAcmeClient

async def main() -> None:
    async with AsyncAcmeClient(token="secret") as client:
        trips = await client.trips.get_trips(origin=a, destination=b, date=when)

asyncio.run(main())

Base URL and servers

The default base URL is taken from the spec's servers (preferring a production entry). Every server is also exported:

from acme_client import DEFAULT_BASE_URL, SERVERS

client = AcmeClient(base_url=SERVERS["Production"])

Authentication

Each security scheme becomes a constructor keyword that is injected via middleware:

Scheme	Keyword	Sent as
http bearer / oauth2 / openIdConnect	token: str	Authorization: Bearer <token>
apiKey (header or query)	<scheme>: str	the named header or query parameter
http basic	<scheme>: tuple[str, str]	Authorization: Basic <base64>

Custom headers, cookies, timeouts

Build the underlying HTTP client yourself and pass it as session= (its type matches the chosen backend — requests.Session by default, httpx.Client, aiohttp.ClientSession, …):

import requests

session = requests.Session()
session.headers["User-Agent"] = "acme/1.0"
client = AcmeClient(session=session)

Errors

Non-2xx responses raise. <package>.exceptions defines a base ApiError plus a subclass per status code (NotFoundError, UnprocessableEntityError, …), with 4xx/5xx falling back to unihttp's ClientError/ServerError.

from acme_client.exceptions import ApiError, NotFoundError

try:
    booking = client.bookings.get_booking(booking_id=bad_id)
except NotFoundError as exc:
    print(exc.status_code, exc.response.data)
except ApiError:
    ...

Middleware

Pass any unihttp middleware; auth and error mapping are composed around it.

from unihttp.middlewares.retry import RetryMiddleware
client = AcmeClient(middleware=[RetryMiddleware(retries=3)])

CLI options

unihttp-openapi-generator generate SPEC [options]

Option	Values (default)
-o, --output-dir	path (required)
--package-name	identifier (required)
--serializer	adaptix · pydantic · msgspec (adaptix)
--client	both · sync · async (both)
--sync-backend	httpx · requests · niquests · zapros (requests)
--async-backend	httpx · aiohttp · niquests · zapros (aiohttp)
--layout	auto · flat · grouped (auto)
--file-layout	single · per-object (single)
--style	declarative · imperative (declarative)
--optional	none · omitted (none) — omitted distinguishes absent from null (adaptix)
--strip-prefix	auto or a dotted prefix to drop from schema names (e.g. io.k8s.api.core.v1.Pod → CoreV1Pod)
--check	run ruff and mypy --strict on the output
--config	TOML config file

Config file

Keep your generation settings in a TOML file so a regenerate is a single command and the configuration lives in version control.

Precedence. For every setting: an explicit CLI flag wins, otherwise the config file, otherwise the built-in default. So you can pin a project's settings in the file and still override one of them ad hoc on the command line:

unihttp-openapi-generator generate                       # use the discovered config
unihttp-openapi-generator generate --serializer msgspec  # override just this one

Discovery order (the first that exists is used):

1. the file passed to --config FILE,
2. unihttp-openapi-generator.toml in the current directory,
3. a [tool.unihttp-openapi-generator] table in pyproject.toml.

Keys mirror the CLI options exactly. spec, output_dir, and package_name are required (from the file or the command line); everything else is optional and falls back to the default shown in the CLI options table. Unknown keys are rejected so typos surface immediately.

A fully annotated unihttp-openapi-generator.toml:

spec = "https://api.example.com/openapi.json"  # path or URL; JSON or YAML
output_dir = "out"                             # where the package is written
package_name = "acme_client"                   # importable package name

serializer = "adaptix"        # adaptix | pydantic | msgspec
client = "both"               # both | sync | async
sync_backend = "requests"     # httpx | requests | niquests | zapros
async_backend = "aiohttp"     # httpx | aiohttp | niquests | zapros
layout = "auto"               # auto | flat | grouped     (client shape)
file_layout = "single"        # single | per-object       (files on disk)
style = "declarative"         # declarative | imperative  (method style)
optional = "none"             # none | omitted            (optional model fields)
strip_prefix = "auto"         # "auto" or a dotted prefix to drop from schema names
check = true                  # run ruff + mypy --strict on the output

Or, to keep it inside an existing project, drop the same keys under a table in pyproject.toml:

[tool.unihttp-openapi-generator]
spec = "openapi.yaml"
output_dir = "out"
package_name = "acme_client"
serializer = "pydantic"
client = "async"

Serializers

	adaptix (default)	pydantic	msgspec
Model type	@dataclass	BaseModel	msgspec.Struct
Field aliasing	full (retort name mapping)	Field(alias=…)	field(name=…)
Query array styles	full	explode only	explode only
Runtime validation	—	yes	yes

adaptix gives the highest fidelity (parameter aliases and all query array styles). pydantic adds runtime validation; msgspec is the fastest.

Generation options

These shape the surface and style of the generated code. All have sensible defaults; reach for them to match an existing codebase or taste.

Client layout — --layout

How methods are exposed on the client.

• flat — every operation is a method on one client class:

  client.get_booking(booking_id=...)
  client.create_booking(body=...)

• grouped — operations are grouped into sub-clients by their OpenAPI tag (nicer for large APIs):

  client.bookings.get_booking(booking_id=...)
  client.payments.create_payment(...)

• auto (default) — flat when the spec has at most one tag, grouped otherwise.

File layout — --file-layout

How the package is split on disk. The import surface is identical either way.

• single (default) — one models.py and one methods/<tag>.py per tag. Fewer, larger files.
• per-object — one file per model/enum and per request method (models/<name>.py, methods/<tag>/<method>.py). Easier to navigate and gives small, focused diffs on regeneration, at the cost of many files. Cross-references between modules are resolved automatically without circular imports.

Method style — --style

How client methods are written.

• declarative (default) — methods are bound from the request classes. Compact; the call signature comes from the request dataclass:

  class BookingsClient:
      get_booking = bind_method(GetBooking)

• imperative — an explicit, fully-typed wrapper per operation. More generated code, but the signature is spelled out for the best editor experience:

  def get_trips(self, *, origin: UUID, destination: UUID, date: datetime,
                page: int = 1, limit: int = 10) -> GetTripsResponse:
      return self.call_method(GetTrips(origin=origin, destination=destination,
                                       date=date, page=page, limit=limit))

Optional fields — --optional

How optional model fields are represented (adaptix only).

• none (default) — T | None = None. Simple, but "field absent" and "field is null" both read as None.

  middle_name: str | None = None

• omitted — Omittable[T] = Omitted(). Distinguishes a field you never set from one set to null; unset fields are dropped from the request body entirely. Useful for PATCH-style APIs where sending null clears a value:

  middle_name: Omittable[str | None] = Omitted()

OpenAPI coverage

• 3.0 and 3.1; JSON or YAML; file or URL; internal and external $ref.
• Schemas: objects, allOf merge, oneOf/anyOf, discriminator (including polymorphic bases), enums and const, formats, nullable, additionalProperties, constraints, recursion, and readOnly (excluded from request bodies).
• Operations: path/query/header parameters with defaults, JSON/form/multipart bodies, file uploads, typed responses, and deprecated.
• Security: apiKey, http bearer/basic, oauth2, openIdConnect.

Limitations

• Response headers are not exposed; methods return the response body.
• deepObject query parameters and full parameter aliasing work on adaptix; on pydantic and msgspec they are limited.
• Swagger / OpenAPI 2.0 is not supported (use the OpenAPI 3 description if a service publishes both, as Kubernetes does).

Development

uv sync
uv run pytest
uv run ruff check src tests
uv run mypy

License

MIT