* Dieses Ergebnis dem Parameter Ihrer *Pfadoperation-Funktion* zuzuweisen.

```mermaid
graph TB

common_parameters(["common_parameters"])
read_items["/items/"]
read_users["/users/"]

common_parameters --> read_items
common_parameters --> read_users
```

Auf diese Weise schreiben Sie gemeinsam genutzten Code nur einmal, und **FastAPI** kümmert sich darum, ihn für Ihre *Pfadoperationen* aufzurufen.

    And it's possible that for your use case, the solution is in one of them.

## Read the Tutorial first

You could still use most of the features in **FastAPI** with the knowledge from the main [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank}.

And the next sections assume you already read it, and assume that you know those main ideas.

## External Courses

* Створіть файл `main.py` з:

```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}
```

<details markdown="1">

```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}
```

<details markdown="1">
<summary>Ya da <code>async def</code>...</summary>

* Créez un fichier `main.py` avec :

```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}
```

<details markdown="1">

### ✍ ⚫️

* ✍ 📁 `main.py` ⏮️:

```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}
```

<details markdown="1">
<summary>⚖️ ⚙️ <code>async def</code>...</summary>

```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}
```

<details markdown="1">

!!! tip
    The next sections are **not necessarily "advanced"**.

    And it's possible that for your use case, the solution is in one of them.

## Read the Tutorial first

The next sections assume you already read the main [Tutorial - User Guide: Security](../../tutorial/security/index.md){.internal-link target=_blank}.

接收到新的请求时，**FastAPI** 执行如下操作：

* 用正确的参数调用依赖项函数（「可依赖项」）
* 获取函数返回的结果
* 把函数返回的结果赋值给*路径操作函数*的参数

```mermaid
graph TB

common_parameters(["common_parameters"])
read_items["/items/"]
read_users["/users/"]

common_parameters --> read_items
common_parameters --> read_users
```

这样，只编写一次代码，**FastAPI** 就可以为多个*路径操作*共享这段代码 。

!!! check "检查"

    注意，无需创建专门的类，并将之传递给 **FastAPI** 以进行「注册」或执行类似的操作。

If something seems interesting and useful to your project, go ahead and check it, but otherwise, you might probably just skip them.

!!! tip