# Sub Applications - Mounts { #sub-applications-mounts }

If you need to have two independent FastAPI applications, with their own independent OpenAPI and their own docs UIs, you can have a main app and "mount" one (or more) sub-application(s).

## Mounting a **FastAPI** application { #mounting-a-fastapi-application }

from fastapi import Depends, FastAPI, Security
from fastapi.security import APIKeyHeader
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()

api_key = APIKeyHeader(name="key")


class User(BaseModel):
    username: str


def get_current_user(oauth_header: str = Security(api_key)):
    user = User(username=oauth_header)
    return user


@app.get("/users/me")

from fastapi import Depends, FastAPI, Security
from fastapi.security import APIKeyHeader
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()

api_key = APIKeyHeader(name="key", description="An API Key Header")


class User(BaseModel):
    username: str


def get_current_user(oauth_header: str = Security(api_key)):
    user = User(username=oauth_header)
    return user

{* ../../docs_src/static_files/tutorial001_py39.py hl[2,6] *}

/// note | Technical Details

You could also use `from starlette.staticfiles import StaticFiles`.

**FastAPI** provides the same `starlette.staticfiles` as `fastapi.staticfiles` just as a convenience for you, the developer. But it actually comes directly from Starlette.

///

### What is "Mounting" { #what-is-mounting }

{* ../../docs_src/static_files/tutorial001_py39.py hl[2,6] *}

/// note | Detalles Técnicos

También podrías usar `from starlette.staticfiles import StaticFiles`.

**FastAPI** proporciona el mismo `starlette.staticfiles` como `fastapi.staticfiles` solo como una conveniencia para ti, el desarrollador. Pero en realidad viene directamente de Starlette.

///

### Qué es "Montar" { #what-is-mounting }

그리고 `yield`를 사용하는 다른 여러 의존성을 필요로 하는 단일 의존성을 가질 수도 있습니다.

원하는 의존성을 원하는 대로 조합할 수 있습니다.

**FastAPI**는 모든 것이 올바른 순서로 실행되도록 보장합니다.

/// note | 기술 세부사항

파이썬의 <a href=“https://docs.python.org/3/library/contextlib.html” class=“external-link” target=“_blank”>Context Managers</a> 덕분에 이 기능이 작동합니다.

**FastAPI**는 이를 내부적으로 컨텍스트 관리자를 사용하여 구현합니다.

///

## `yield`와 `HTTPException`를 사용하는 의존성

You could also use `from starlette.testclient import TestClient`.

**FastAPI** provides the same `starlette.testclient` as `fastapi.testclient` just as a convenience for you, the developer. But it comes directly from Starlette.

///

/// tip

    errors in your code.

    Read more about it in the
    [FastAPI docs for Handling Errors](https://fastapi.tiangolo.com/tutorial/handling-errors/).

    ## Example

    ```python
    from fastapi import FastAPI, HTTPException

    app = FastAPI()

    items = {"foo": "The Foo Wrestlers"}


    @app.get("/items/{item_id}")
    async def read_item(item_id: str):

# 高级用户指南

## 额外特性

主要的教程 [教程 - 用户指南](../tutorial/index.md){.internal-link target=_blank} 应该足以让你了解 **FastAPI** 的所有主要特性。

你会在接下来的章节中了解到其他的选项、配置以及额外的特性。

/// tip

接下来的章节**并不一定是**「高级的」。

而且对于你的使用场景来说，解决方案很可能就在其中。

///

## 先阅读教程

你可能仍会用到 **FastAPI** 主教程 [教程 - 用户指南](../tutorial/index.md){.internal-link target=_blank} 中的大多数特性。

import importlib
import runpy
import sys
import unittest

import pytest
from fastapi.testclient import TestClient

MOD_NAME = "docs_src.debugging.tutorial001_py39"


@pytest.fixture(name="client")
def get_client():
    mod = importlib.import_module(MOD_NAME)
    client = TestClient(mod.app)
    return client


def test_uvicorn_run_is_not_called_on_import():
    if sys.modules.get(MOD_NAME):