from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(default=None, title="Query string", min_length=3),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[str, None], Query(alias="item-query")] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from pydantic import BaseModel as BaseModelV2
from pydantic.v1 import BaseModel


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    size: float


class ItemV2(BaseModelV2):
    name: str
    description: Union[str, None] = None
    size: float


app = FastAPI()


@app.post("/items/", response_model=ItemV2)
async def create_item(item: Item):

app = FastAPI()


@app.post("/files/")
async def create_file(file: bytes | None = File(default=None)):
    if not file:
        return {"message": "No file sent"}
    else:
        return {"file_size": len(file)}


@app.post("/uploadfile/")
async def create_upload_file(file: UploadFile | None = None):
    if not file:
        return {"message": "No upload file sent"}
    else:

/// note | Заметка

FastAPI понимает, что значение `q` не является обязательным из-за значения по умолчанию `= None`.

Аннотации типов `str | None` (Python 3.10+) или `Union[str, None]` (Python 3.9+) не используются FastAPI для определения обязательности; он узнает, что параметр не обязателен, потому что у него есть значение по умолчанию `= None`.

Но добавление аннотаций типов позволит вашему редактору кода лучше вас поддерживать и обнаруживать ошибки.

from fastapi import FastAPI
from pydantic import BaseModel, EmailStr

app = FastAPI()


class UserIn(BaseModel):
    username: str
    password: str
    email: EmailStr
    full_name: Union[str, None] = None


# Don't do this in production!
@app.post("/user/")
async def create_user(user: UserIn) -> UserIn:

import org.apache.maven.project.MavenProject;

/**
 * Instances of this interface retrieve and store data for the --resume / -r feature. This data is used to ensure newer
 * builds of the same project, that have the -r command-line flag, skip successfully built projects during earlier
 * invocations of Maven.
 */
public interface BuildResumptionDataRepository {
    /**

    }
  }

  /**
   * Reads the first line from a file. The line does not include line-termination characters, but
   * does include other leading and trailing whitespace.
   *
   * @param file the file to read from
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @return the first line, or null if the file is empty

from typing import Union

from fastapi import FastAPI


@dataclass
class Item:
    name: str
    price: float
    tags: list[str] = field(default_factory=list)
    description: Union[str, None] = None
    tax: Union[float, None] = None


app = FastAPI()


@app.get("/items/next", response_model=Item)
async def read_next_item():
    return {
        "name": "Island In The Moon",
        "price": 12.99,

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None
    tags: set[str] = set()


@app.post("/items/", response_model=Item, tags=["items"])
async def create_item(item: Item):
    return item


@app.get("/items/", tags=["items"])
async def read_items():