from typing import Annotated, Union

from fastapi import FastAPI, Header

app = FastAPI()


@app.get("/items/")
async def read_items(user_agent: Annotated[Union[str, None], Header()] = None):

from typing import Union

from fastapi import FastAPI, Header
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(user_agent: Annotated[Union[str, None], Header()] = None):

`Header` ✔️ 🐥 ➕ 🛠️ 🔛 🔝 ⚫️❔ `Path`, `Query` & `Cookie` 🚚.

🌅 🐩 🎚 🎏 "🔠" 🦹, 💭 "➖ 🔣" (`-`).

✋️ 🔢 💖 `user-agent` ❌ 🐍.

, 🔢, `Header` 🔜 🗜 🔢 📛 🦹 ⚪️➡️ 🎦 (`_`) 🔠 (`-`) ⚗ & 📄 🎚.

, 🇺🇸🔍 🎚 💼-😛,, 👆 💪 📣 👫 ⏮️ 🐩 🐍 👗 (💭 "🔡").

, 👆 💪 ⚙️ `user_agent` 👆 🛎 🔜 🐍 📟, ↩️ 💆‍♂ 🎯 🥇 🔤 `User_Agent` ⚖️ 🕳 🎏.

🚥 🤔 👆 💪 ❎ 🏧 🛠️ 🎦 🔠, ⚒ 🔢 `convert_underscores` `Header` `False`:

=== "🐍 3️⃣.6️⃣ & 🔛"

Portanto, você pode usar `user_agent` como faria normalmente no código Python, em vez de precisar colocar as primeiras letras em maiúsculas como `User_Agent` ou algo semelhante.

Se por algum motivo você precisar desabilitar a conversão automática de sublinhados para hífens, defina o parâmetro `convert_underscores` de `Header` para `False`:

But a variable like `user-agent` is invalid in Python.

So, by default, `Header` will convert the parameter names characters from underscore (`_`) to hyphen (`-`) to extract and document the headers.

Also, HTTP headers are case-insensitive, so, you can declare them with standard Python style (also known as "snake_case").

Aber eine Variable wie `user-agent` ist in Python nicht gültig.

Darum wird `Header` standardmäßig in Parameternamen den Unterstrich (`_`) zu einem Bindestrich (`-`) konvertieren.

HTTP-Header sind außerdem unabhängig von Groß-/Kleinschreibung, darum können Sie sie mittels der Standard-Python-Schreibweise deklarieren (auch bekannt als "snake_case").

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  - author: New Relic
    author_link: https://newrelic.com
    link: https://newrelic.com/instant-observability/fastapi/e559ec64-f765-4470-a15f-1901fcebb468
    title: How to monitor FastAPI application performance using Python agent
  - author: Jean-Baptiste Rocher
    author_link: https://hashnode.com/@jibrocher
    link: https://dev.indooroutdoor.io/series/fastapi-react-poll-app
    title: Building the Poll App From Django Tutorial With FastAPI And React

* 📝 Add link to New Relic article: "How to monitor FastAPI application performance using Python agent". PR [#5260](https://github.com/tiangolo/fastapi/pull/5260) by [@sjyothi54](https://github.com/sjyothi54).

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