### Technical Details: `root_path`

When you mount a sub-application as described above, FastAPI will take care of communicating the mount path for the sub-application using a mechanism from the ASGI specification called a `root_path`.

That way, the sub-application will know to use that path prefix for the docs UI.

from fastapi import FastAPI, Request

app = FastAPI()


@app.get("/app")
def read_main(request: Request):

🚥 👆 🔄 🔗 ⏮️ 🙆 2️⃣ 👩‍💻 🔢, 👫 🔜 👷 ☑, ↩️ 🖥 🔜 💪 💬 🔠 🎯 📱 ⚖️ 🎧-📱.

### 📡 ℹ: `root_path`

🕐❔ 👆 🗻 🎧-🈸 🔬 🔛, FastAPI 🔜 ✊ 💅 🔗 🗻 ➡ 🎧-🈸 ⚙️ 🛠️ ⚪️➡️ 🔫 🔧 🤙 `root_path`.

👈 🌌, 🎧-🈸 🔜 💭 ⚙️ 👈 ➡ 🔡 🩺 🎚.

& 🎧-🈸 💪 ✔️ 🚮 👍 📌 🎧-🈸 & 🌐 🔜 👷 ☑, ↩️ FastAPI 🍵 🌐 👉 `root_path`Ⓜ 🔁.

import pytest
from httpx import AsyncClient

from .main import app


@pytest.mark.anyio
async def test_root():
    async with AsyncClient(app=app, base_url="http://test") as ac:
        response = await ac.get("/")
    assert response.status_code == 200

client = TestClient(app)


def test_main():
    response = client.get("/app")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello World", "root_path": "/api/v1"}


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200
    assert response.json() == {
        "openapi": "3.1.0",

    response = client.get("/files/home/johndoe/myfile.txt")
    print(response.content)
    assert response.status_code == 200, response.text
    assert response.json() == {"file_path": "home/johndoe/myfile.txt"}


def test_root_file_path():
    response = client.get("/files//home/johndoe/myfile.txt")
    print(response.content)
    assert response.status_code == 200, response.text
    assert response.json() == {"file_path": "/home/johndoe/myfile.txt"}

                ("files", ("test2.txt", file2)),
            ),
        )
    assert response.status_code == 200, response.text
    assert response.json() == {"filenames": ["test.txt", "test2.txt"]}


def test_get_root():
    client = TestClient(app)
    response = client.get("/")
    assert response.status_code == 200, response.text
    assert b"<form" in response.content


def test_openapi_schema():

                ("files", ("test2.txt", file2)),
            ),
        )
    assert response.status_code == 200, response.text
    assert response.json() == {"filenames": ["test.txt", "test2.txt"]}


def test_get_root():
    client = TestClient(app)
    response = client.get("/")
    assert response.status_code == 200, response.text
    assert b"<form" in response.content


def test_openapi_schema():

            ),
        )
    assert response.status_code == 200, response.text
    assert response.json() == {"filenames": ["test.txt", "test2.txt"]}


@needs_py39
def test_get_root(app: FastAPI):
    client = TestClient(app)
    response = client.get("/")
    assert response.status_code == 200, response.text
    assert b"<form" in response.content


@needs_py39

### Hozd létre

* Hozz létre a `main.py` fájlt a következő tartalommal:

```Python
from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

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