By doing it this way, we can put it in a `with` block, and that way, ensure that it is closed after finishing.

!!! tip
    Notice that here as we are using standard `open()` that doesn't support `async` and `await`, we declare the path operation with normal `def`.

### `FileResponse`

Asynchronously streams a file as the response.

```JSON
{
    "message": "Hello World",
    "root_path": "/api/v1"
}
```

!!! tip
    Notice that even though you are accessing it at `http://127.0.0.1:8000/app` it shows the `root_path` of `/api/v1`, taken from the option `--root-path`.

!!! tip
    Notice that the values you return are SQLAlchemy models, or lists of SQLAlchemy models.

    But as all the *path operations* have a `response_model` with Pydantic *models* / schemas using `orm_mode`, the data declared in your Pydantic models will be extracted from them and returned to the client, with all the normal filtering and validation.

!!! tip

But if your connection to the server is lost, the **running process** will probably die.

And if the server is restarted (for example after updates, or migrations from the cloud provider) you probably **won't notice it**. And because of that, you won't even know that you have to restart the process manually. So, your API will just stay dead. 😱

### Run Automatically on Startup

read_users["/users/"]

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

This way you write shared code once and **FastAPI** takes care of calling it for your *path operations*.

!!! check
    Notice that you don't have to create a special class and pass it somewhere to **FastAPI** to "register" it or anything similar.

    You just pass it to `Depends` and **FastAPI** knows how to do the rest.

```Python
something()
```

or

```Python
something(some_argument, some_keyword_argument="foo")
```

then it is a "callable".

## Classes as dependencies

You might notice that to create an instance of a Python class, you use that same syntax.

For example:

```Python
class Cat:
    def __init__(self, name: str):
        self.name = name


fluffy = Cat(name="Mr Fluffy")

    ```

=== "Python 3.8+"

    ```Python hl_lines="10"
    {!> ../../../docs_src/query_params_str_validations/tutorial002_an.py!}
    ```

Notice that the default value is still `None`, so the parameter is still optional.

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *

By doing that, your editor can provide support even while processing items from the list:

<img src="/img/python-types/image05.png">

Without types, that's almost impossible to achieve.

Notice that the variable `item` is one of the elements in the list `items`.

And still, the editor knows it is a `str`, and provides support for that.

#### Tuple and Set

    {!> ../../../docs_src/response_model/tutorial001_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="17  22  24-27"
    {!> ../../../docs_src/response_model/tutorial001.py!}
    ```

!!! note
    Notice that `response_model` is a parameter of the "decorator" method (`get`, `post`, etc). Not of your *path operation function*, like all the parameters and body.