It is very simple and intuitive. It's designed to be easily extensible, and have modular components.

It has:

* Seriously impressive performance.
* WebSocket support.
* In-process background tasks.
* Startup and shutdown events.
* Test client built on HTTPX.

## Separating tests

In a real application, you probably would have your tests in a different file.

And your **FastAPI** application might also be composed of several files/modules, etc.

### **FastAPI** app file

Let's say you have a file structure as described in [Bigger Applications](bigger-applications.md){.internal-link target=_blank}:

```
.
├── app
│   ├── __init__.py

 ╭─ <font color="#8AE234"><b>Python module file</b></font> ─╮
 │                      │
 │  🐍 main.py          │
 │                      │
 ╰──────────────────────╯

<font color="#3465A4">INFO    </font> Importing module <font color="#4E9A06">main</font>
<font color="#3465A4">INFO    </font> Found importable FastAPI app

 ╭─ <font color="#8AE234"><b>Python module file</b></font> ─╮
 │                      │
 │  🐍 main.py          │
 │                      │
 ╰──────────────────────╯

<font color="#3465A4">INFO    </font> Importing module <font color="#4E9A06">main</font>
<font color="#3465A4">INFO    </font> Found importable FastAPI app

<span style="color: green;">INFO</span>:     Application startup complete.
```

</div>

!!! note "備考"
    `uvicorn main:app`は以下を示します:

    * `main`: `main.py`ファイル (Python "module")。
    * `app`:  `main.py`内部で作られるobject（`app = FastAPI()`のように記述される）。
    * `--reload`: コードの変更時にサーバーを再起動させる。開発用。

出力には次のような行があります:

```hl_lines="4"

</div>

<details markdown="1">
<summary>Informazioni sul comando <code>uvicorn main:app --reload</code>...</summary>

Vediamo il comando `uvicorn main:app` in dettaglio:

* `main`: il file `main.py` (il "modulo" Python).
* `app`: l'oggetto creato dentro `main.py` con la riga di codice `app = FastAPI()`.
* `--reload`: ricarica il server se vengono rilevati cambiamenti del codice. Usalo solo durante la fase di sviluppo.

</details>

    ```

    To learn more about Python Packages and Modules, read <a href="https://docs.python.org/3/tutorial/modules.html" class="external-link" target="_blank">the official Python documentation about Modules</a>.

### Avoid name collisions

We are importing the submodule `items` directly, instead of importing just its variable `router`.

This is because we also have another variable named `router` in the submodule `users`.

]

[tool.mypy]
strict = true

[[tool.mypy.overrides]]
module = "fastapi.concurrency"
warn_unused_ignores = false
ignore_missing_imports = true

[[tool.mypy.overrides]]
module = "fastapi.tests.*"
ignore_missing_imports = true
check_untyped_defs = true

[[tool.mypy.overrides]]
module = "docs_src.*"
disallow_incomplete_defs = false
disallow_untyped_defs = false

These types that have internal types are called "**generic**" types. And it's possible to declare them, even with their internal types.

To declare those types and the internal types, you can use the standard Python module `typing`. It exists specifically to support these type hints.

#### Newer versions of Python

    ```

    第二个版本是「绝对导入」：

    ```Python
    from app.routers import items, users
    ```

    要了解有关 Python 包和模块的更多信息，请查阅<a href="https://docs.python.org/3/tutorial/modules.html" class="external-link" target="_blank">关于 Modules 的 Python 官方文档</a>。

### 避免名称冲突

我们将直接导入 `items` 子模块，而不是仅导入其 `router` 变量。

这是因为我们在 `users` 子模块中也有另一个名为 `router` 的变量。

如果我们一个接一个地导入，例如：

```Python