* If you didn't use FastAPI and used Starlette directly (or another tool, like Sanic, Flask, Responder, etc) you would have to implement all the data validation and serialization yourself. So, your final application would still have the same overhead as if it was...

    assert response.json() == "Listen to the Bar Fighters"
    response = client.put("/get-or-create-task/bar")
    assert response.status_code == 201, response.text

from typing_extensions import Annotated

app = FastAPI()


class InternalError(Exception):
    pass


def get_username():
    try:
        yield "Rick"
    except InternalError:
        print("Oops, we didn't raise again, Britney 😱")


@app.get("/items/{item_id}")
def get_item(item_id: str, username: Annotated[str, Depends(get_username)]):
    if item_id == "portal-gun":
        raise InternalError(

body:
  - type: markdown
    attributes:
      value: |
        Thanks for your interest in FastAPI! 🚀

        If you are not @tiangolo or he didn't ask you directly to create an issue here, please start the conversation in a [Question in GitHub Discussions](https://github.com/tiangolo/fastapi/discussions/categories/questions) instead.
  - type: checkboxes
    id: privileged

Body schema definitions didn't use the same Python type hints like Pydantic, it was a bit more similar to Marshmallow, so, editor support wouldn't be as good, but still, APIStar was the best available option.

It had the best performance benchmarks at the time (only surpassed by Starlette).

At first, it didn't have an automatic API documentation web UI, but I knew I could add Swagger UI to it.

!!! check
    So, with the same Python type declaration, **FastAPI** gives you data validation.

    Notice that the error also clearly states exactly the point where the validation didn't pass.

    This is incredibly helpful while developing and debugging code that interacts with your API.

## Documentation

tasks = {"foo": "Listen to the Bar Fighters"}


@app.put("/get-or-create-task/{task_id}", status_code=200)
def get_or_create_task(task_id: str, response: Response):
    if task_id not in tasks:
        tasks[task_id] = "This didn't exist before"
        response.status_code = status.HTTP_201_CREATED

          required: true
        - label: I searched the FastAPI documentation, with the integrated search.
          required: true
        - label: I already searched in Google "How to X in FastAPI" and didn't find any information.
          required: true
        - label: I already read and followed all the tutorial in the docs and didn't find an answer.
          required: true

app = FastAPI()


class InternalError(Exception):
    pass


def get_username():
    try:
        yield "Rick"
    except InternalError:
        print("Oops, we didn't raise again, Britney 😱")


@app.get("/items/{item_id}")
def get_item(item_id: str, username: str = Depends(get_username)):
    if item_id == "portal-gun":
        raise InternalError(

app = FastAPI()


class InternalError(Exception):
    pass


def get_username():
    try:
        yield "Rick"
    except InternalError:
        print("Oops, we didn't raise again, Britney 😱")


@app.get("/items/{item_id}")
def get_item(item_id: str, username: Annotated[str, Depends(get_username)]):
    if item_id == "portal-gun":
        raise InternalError(