API Schemas

Starlette supports generating API schemas, such as the widely used OpenAPI specification. (Formerly known as "Swagger".)

Schema generation works by inspecting the routes on the application through app.routes, and using the docstrings or other attributes on the endpoints in order to determine a complete API schema.

Starlette is not tied to any particular schema generation or validation tooling, but includes a simple implementation that generates OpenAPI schemas based on the docstrings.

from starlette.applications import Starlette
from starlette.routing import Route
from starlette.schemas import SchemaGenerator


schemas = SchemaGenerator(
    {"openapi": "3.0.0", "info": {"title": "Example API", "version": "1.0"}}
)

def list_users(request):
    """
    responses:
      200:
        description: A list of users.
        examples:
          [{"username": "tom"}, {"username": "lucy"}]
    """
    raise NotImplementedError()


def create_user(request):
    """
    responses:
      200:
        description: A user.
        examples:
          {"username": "tom"}
    """
    raise NotImplementedError()


def openapi_schema(request):
    return schemas.OpenAPIResponse(request=request)


routes = [
    Route("/users", endpoint=list_users, methods=["GET"]),
    Route("/users", endpoint=create_user, methods=["POST"]),
    Route("/schema", endpoint=openapi_schema, include_in_schema=False)
]

app = Starlette(routes=routes)

We can now access an OpenAPI schema at the "/schema" endpoint.

You can generate the API Schema directly with .get_schema(routes):

schema = schemas.get_schema(routes=app.routes)
assert schema == {
    "openapi": "3.0.0",
    "info": {"title": "Example API", "version": "1.0"},
    "paths": {
        "/users": {
            "get": {
                "responses": {
                    200: {
                        "description": "A list of users.",
                        "examples": [{"username": "tom"}, {"username": "lucy"}],
                    }
                }
            },
            "post": {
                "responses": {
                    200: {"description": "A user.", "examples": {"username": "tom"}}
                }
            },
        },
    },
}

You might also want to be able to print out the API schema, so that you can use tooling such as generating API documentation.

if __name__ == '__main__':
    assert sys.argv[-1] in ("run", "schema"), "Usage: example.py [run|schema]"

    if sys.argv[-1] == "run":
        uvicorn.run("example:app", host='0.0.0.0', port=8000)
    elif sys.argv[-1] == "schema":
        schema = schemas.get_schema(routes=app.routes)
        print(yaml.dump(schema, default_flow_style=False))

Third party packages

starlette-apispec

Easy APISpec integration for Starlette, which supports some object serialization libraries.