しかし例外ハンドラで処理されない例外を発生させた場合は、依存関係の終了コードで処理されます。

## コンテキストマネージャ

### 「コンテキストマネージャ」とは

「コンテキストマネージャ」とは、`with`文の中で使用できるPythonオブジェクトのことです。

例えば、<a href="https://docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files" class="external-link" target="_blank">ファイルを読み込むには`with`を使用することができます</a>:

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

    In many cases, OAuth2 with scopes can be an overkill.

    But if you know you need it, or you are curious, keep reading.

## OAuth2 scopes and OpenAPI

The OAuth2 specification defines "scopes" as a list of strings separated by spaces.

The content of each of these strings can have any format, but should not contain spaces.

* **Intuitive**: Great editor support. <abbr title="also known as auto-complete, autocompletion, IntelliSense">Completion</abbr> everywhere. Less time debugging.
* **Easy**: Designed to be easy to use and learn. Less time reading docs.
* **Short**: Minimize code duplication. Multiple features from each parameter declaration. Fewer bugs.
* **Robust**: Get production-ready code. With automatic interactive documentation.

„Kontextmanager“ (Englisch „Context Manager“) sind bestimmte Python-Objekte, die Sie in einer `with`-Anweisung verwenden können.

Beispielsweise können Sie <a href="https://docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files" class="external-link" target="_blank">`with` verwenden, um eine Datei auszulesen</a>:

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

gain (about 100 nanoseconds), please note that in **FastAPI** the effect would be quite opposite. In these cases, it's better to use `async def` unless your *path operation functions* use code that performs blocking <abbr title="Input/Output: disk reading or writing, network communications.">I/O</abbr>.

Still, in both situations, chances are that **FastAPI** will [still be faster](index.md#performance){.internal-link target=_blank} than (or at least comparable to) your previous framework....

### Create Pydantic *models* / schemas for reading / returning

Now create Pydantic *models* (schemas) that will be used when reading data, when returning it from the API.

For example, before creating an item, we don't know what will be the ID assigned to it, but when reading it (when returning it from the API) we will already know its ID.

### Creating the `Settings` only once with `lru_cache`

Reading a file from disk is normally a costly (slow) operation, so you probably want to do it only once and then re-use the same settings object, instead of reading it for each request.

But every time we do:

```Python
Settings()
```

The **Advanced User Guide**, builds on this, uses the same concepts, and teaches you some extra features.

But you should first read the **Tutorial - User Guide** (what you are reading right now).

* **Intuitive**: Great editor support. <abbr title="also known as auto-complete, autocompletion, IntelliSense">Completion</abbr> everywhere. Less time debugging.
* **Easy**: Designed to be easy to use and learn. Less time reading docs.
* **Short**: Minimize code duplication. Multiple features from each parameter declaration. Fewer bugs.
* **Robust**: Get production-ready code. With automatic interactive documentation.

### What are "Context Managers"

"Context Managers" are any of those Python objects that you can use in a `with` statement.

For example, <a href="https://docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files" class="external-link" target="_blank">you can use `with` to read a file</a>:

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```