In many cases your application could need some external settings or configurations, for example secret keys, database credentials, credentials for email services, etc.

Most of these settings are variable (can change), like database URLs. And many could be sensitive, like secrets.

For this reason it's common to provide them in environment variables that are read by the application.

/// tip

In many cases, when you use regular Pydantic models without customizations, you will be able to automate most of the process of migrating from Pydantic v1 to Pydantic v2.

You can use <a href="https://github.com/pydantic/bump-pydantic" class="external-link" target="_blank">`bump-pydantic`</a> from the same Pydantic team.

This tool will help you to automatically change most of the code that needs to be changed.

# Tutorial - User Guide { #tutorial-user-guide }

This tutorial shows you how to use **FastAPI** with most of its features, step by step.

Each section gradually builds on the previous ones, but it's structured to separate topics, so that you can go directly to any specific one to solve your specific API needs.

It is also built to work as a future reference so you can come back and see exactly what you need.

## Run the code { #run-the-code }

///

If you are using `pip` to install packages (it comes by default with Python), you should **upgrade** it to the latest version.

Many exotic errors while installing a package are solved by just upgrading `pip` first.

/// tip

You would normally do this **once**, right after you create the virtual environment.

///

Make sure the virtual environment is active (with the command above) and then run:

But in most of the cases where we need to do something like this, we want the model just to **filter/remove** some of the data as in this example.

## Quick Start

/// tip

You don't need to see the code in `./scripts/docs.py`, you just use it in the command line.

///

All the documentation is in Markdown format in the directory `./docs/en/`.

Many of the tutorials have blocks of code.

In most of the cases, these blocks of code are actual complete applications that can be run as is.

http://localhost:8000/items/
```

the default of `q` will be: `["foo", "bar"]` and your response will be:

```JSON
{
  "q": [
    "foo",
    "bar"
  ]
}
```

#### Using just `list` { #using-just-list }

You can also use `list` directly instead of `list[str]`:

{* ../../docs_src/query_params_str_validations/tutorial013_an_py39.py hl[9] *}

/// note

For the other languages, confirm that:

* The title is correct following the instructions above.
* It has the labels `lang-all` and `lang-{lang code}`.
* The PR changes only one Markdown file adding a translation.
    * Or in some cases, at most two files, if they are small, for the same language, and people reviewed them.

        Thanks for your interest in FastAPI! 🚀

        Please follow these instructions, fill every question, and do every step. 🙏

        I'm asking this because answering questions and solving problems in GitHub is what consumes most of the time.

        I end up not being able to add new features, fix bugs, review pull requests, etc. as fast as I wish because I have to spend too much time handling questions.