One of the main features needed by API systems is data "<abbr title="also called marshalling, conversion">serialization</abbr>" which is taking data from the code (Python) and converting it into something that can be sent through the network. For example, converting an object containing data from a database into a JSON object. Converting `datetime` objects into strings, etc.

        client.get("/items/invalidnone")


def test_valid_none_data():
    response = client.get("/items/validnone")
    data = response.json()
    assert response.status_code == 200
    assert data == {"name": "invalid", "price": 3.2, "owner_ids": None}


def test_valid_none_none():
    response = client.get("/items/validnone", params={"send_none": "true"})
    data = response.json()
    assert response.status_code == 200

    * 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...

                    "required": ["data"],
                    "type": "object",
                    "properties": {"data": {"$ref": "#/components/schemas/Product"}},
                },
                "Body_create_shop_shops_post": {
                    "title": "Body_create_shop_shops_post",
                    "required": ["data"],
                    "type": "object",

## Recap

With **FastAPI**, by using short, intuitive and standard Python type declarations, you get:

* Editor support: error checks, autocompletion, etc.
* Data "<abbr title="converting the string that comes from an HTTP request into Python data">parsing</abbr>"
* Data validation
* API annotation and automatic documentation

And you only have to declare them once.

    data = {"username": username, "password": password}
    if scope:
        data["scope"] = scope
    response = client.post("/token", data=data)
    content = response.json()
    access_token = content.get("access_token")
    return access_token


def test_login():
    response = client.post("/token", data={"username": "johndoe", "password": "secret"})

            generated OpenAPI, but currently it doesn't affect the parsing of the data.
            """
        ),
    ] = "multipart/form-data",
    alias: Annotated[
        Optional[str],
        Doc(
            """
            An alternative name for the parameter field.

            This will be used to extract the data and for the generated OpenAPI.

    return current_user


@app.post("/token")
async def login(form_data: Annotated[OAuth2PasswordRequestForm, Depends()]):
    user_dict = fake_users_db.get(form_data.username)
    if not user_dict:
        raise HTTPException(status_code=400, detail="Incorrect username or password")
    user = UserInDB(**user_dict)
    hashed_password = fake_hash_password(form_data.password)
    if not hashed_password == user.hashed_password:

):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(
            f"Session cookie or query token value is: {cookie_or_token}"
        )
        if q is not None:
            await websocket.send_text(f"Query parameter q is: {q}")

class User(BaseModel):
    id: int
    name: str = "John Doe"
    signup_ts: Union[datetime, None] = None
    friends: List[int] = []


external_data = {
    "id": "123",
    "signup_ts": "2017-06-01 12:22",
    "friends": [1, "2", b"3"],
}
user = User(**external_data)
print(user)
# > User id=123 name='John Doe' signup_ts=datetime.datetime(2017, 6, 1, 12, 22) friends=[1, 2, 3]
print(user.id)