### ⚙️ `app.dependency_overrides` 🔢

👫 💼, 👆 **FastAPI** 🈸 ✔️ 🔢 `app.dependency_overrides`, ⚫️ 🙅 `dict`.

🔐 🔗 🔬, 👆 🚮 🔑 ⏮️ 🔗 (🔢), & 💲, 👆 🔗 🔐 (➕1️⃣ 🔢).

& ⤴️ **FastAPI** 🔜 🤙 👈 🔐 ↩️ ⏮️ 🔗.

```Python hl_lines="28-29  32"
{!../../docs_src/dependency_testing/tutorial001.py!}
```

/// tip

👆 💪 ⚒ 🔗 🔐 🔗 ⚙️ 🙆 👆 **FastAPI** 🈸.

from typing import Union

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


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


class UserInDB(BaseModel):
    username: str
    hashed_password: str

from typing import Set, Union

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


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


@app.post("/items/", response_model=Item, summary="Create an item")
async def create_item(item: Item):
    """
    Create an item with all the information:

from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


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


@app.post(
    "/items/",
    response_model=Item,
    summary="Create an item",
    response_description="The created item",
)

from datetime import datetime, timezone

from fastapi import FastAPI
from fastapi.testclient import TestClient
from pydantic import BaseModel

from .utils import needs_pydanticv1, needs_pydanticv2


@needs_pydanticv2
def test_pydanticv2():
    from pydantic import field_serializer

    class ModelWithDatetimeField(BaseModel):
        dt_field: datetime

        @field_serializer("dt_field")

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float = 10.5


items = {
    "foo": {"name": "Foo", "price": 50.2},
    "bar": {"name": "Bar", "description": "The Bar fighters", "price": 62, "tax": 20.2},
    "baz": {
        "name": "Baz",
        "description": "There goes my baz",

# Development - Contributing

First, you might want to see the basic ways to [help FastAPI and get help](help-fastapi.md){.internal-link target=_blank}.

## Developing

If you already cloned the <a href="https://github.com/fastapi/fastapi" class="external-link" target="_blank">fastapi repository</a> and you want to deep dive in the code, here are some guidelines to set up your environment.

### Virtual environment

from fastapi import Depends, FastAPI
from fastapi.security import HTTPBasic, HTTPBasicCredentials

app = FastAPI()

security = HTTPBasic()


@app.get("/users/me")
def read_current_user(credentials: HTTPBasicCredentials = Depends(security)):

この場合、HTTPヘッダー `Content-Type` には `application/json` がセットされます。

そして、OpenAPIにはそのようにドキュメントされます。

///

/// tip | "豆知識"

`ORJSONResponse` は、現在はFastAPIのみで利用可能で、Starletteでは利用できません。

///

## HTMLレスポンス

**FastAPI** からHTMLを直接返す場合は、`HTMLResponse` を使います。

* `HTMLResponse` をインポートする。
* *path operation* のパラメータ `content_type` に `HTMLResponse` を渡す。

```Python hl_lines="2  7"

from fastapi import FastAPI
from fastapi.responses import StreamingResponse

app = FastAPI()


async def fake_video_streamer():
    for i in range(10):
        yield b"some fake video bytes"


@app.get("/")
async def main():