@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}
```

<details markdown="1">
<summary>Albo użyj <code>async def</code>...</summary>

Jeżeli twój kod korzysta z `async` / `await`, użyj `async def`:

```Python hl_lines="9  14"
from typing import Union

@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}
```

<details markdown="1">
<summary>Или используйте <code>async def</code>...</summary>

Если ваш код использует `async` / `await`, используйте `async def`:

```Python hl_lines="9  14"
from typing import Union

INFO:     Application startup complete.
```

</div>

<details markdown="1">
<summary>关于 <code>uvicorn main:app --reload</code> 命令......</summary>

 `uvicorn main:app` 命令含义如下:

* `main`：`main.py` 文件（一个 Python "模块"）。
* `app`：在 `main.py` 文件中通过 `app = FastAPI()` 创建的对象。
* `--reload`：让服务器在更新代码后重新启动。仅在开发时使用该选项。

</details>

### 检查

</div>

That would work for most of the cases. 😎

You could use that command for example to start your **FastAPI** app in a container, in a server, etc.

## ASGI Servers

Let's go a little deeper into the details.

FastAPI uses a standard for building Python web frameworks and servers called <abbr title="Asynchronous Server Gateway Interface">ASGI</abbr>. FastAPI is an ASGI web framework.

<span style="color: green;">INFO</span>:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
```

</div>

If you use Hypercorn, it also has the option `--root-path`.

!!! note "Technical Details"
    The ASGI specification defines a `root_path` for this use case.

    And the `--root-path` command line option provides that `root_path`.

### Checking the current `root_path`

### Step 1: import `FastAPI`

```Python hl_lines="1"
{!../../../docs_src/first_steps/tutorial001.py!}
```

`FastAPI` is a Python class that provides all the functionality for your API.

!!! note "Technical Details"
    `FastAPI` is a class that inherits directly from `Starlette`.

    You can use all the <a href="https://www.starlette.io/" class="external-link" target="_blank">Starlette</a> functionality with `FastAPI` too.

@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}
```

<details markdown="1">
<summary>O usa <code>async def</code>...</summary>

Si tu código usa `async` / `await`, usa `async def`:

```Python hl_lines="7  12"
from fastapi import FastAPI
from typing import Union

@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}
```

<details markdown="1">
<summary>Vagy használd az <code>async def</code>-et...</summary>

Ha a kódod `async` / `await`-et, használ `async def`:

```Python hl_lines="9  14"
from typing import Union

**Technical Details**: If you want to know more of the technical details you can check out the PR description [#4575](https://github.com/tiangolo/fastapi/pull/4575).

### Internal

<img src="/img/deployment/concepts/process-ram.svg">

And of course, the same machine would probably have **other processes** running as well, apart from your application.

An interesting detail is that the percentage of the **CPU used** by each process can **vary** a lot over time, but the **memory (RAM)** normally stays more or less **stable**.