It had automatic data validation, data serialization and OpenAPI schema generation based on the same type hints in several places.

## Be Nice

First of all, be nice. 😊

You probably are super nice if you were added to the team, but it's worth mentioning it. 🤓

### When Things are Difficult

When things are great, everything is easier, so that doesn't need much instructions. But when things are difficult, here are some guidelines.

* A particular program while it is **running** on the operating system.
    * This doesn't refer to the file, nor to the code, it refers **specifically** to the thing that is being **executed** and managed by the operating system.

Activating a virtual environment also changes a couple of other things, but this is one of the most important things it does.

## Checking a Virtual Environment { #checking-a-virtual-environment }

When you check if a virtual environment is active, for example with:

//// tab | Linux, macOS, Windows Bash

     * parameters, and as it turns out Firefox and Chrome actually do rather different things, and
     * both say in their comments that they're not really sure what the right approach is. We go
     * with Chrome's behavior (which also experimentally seems to match what IE does), but if you
     * actually want to have a good chance of things working, please avoid double-quotes, newlines,
     * percent signs, and the like in your field names.

The JWT specification says that there's a key `sub`, with the subject of the token.

It's optional to use it, but that's where you would put the user's identification, so we are using it here.

JWT might be used for other things apart from identifying a user and allowing them to perform operations directly on your API.

For example, you could identify a "car" or a "blog post".

### Tests { #tests }

* Help me check that the PR has **tests**.

* Check that the tests **fail** before the PR. 🚨

* Then check that the tests **pass** after the PR. ✅

* Many PRs don't have tests, you can **remind** them to add tests, or you can even **suggest** some tests yourself. That's one of the things that consume most time and you can help a lot with that.

If you generate a client for a FastAPI app using tags, it will normally also separate the client code based on the tags.

This way, you will be able to have things ordered and grouped correctly for the client code:

<img src="/img/tutorial/generate-clients/image06.png">

In this case, you have:

* `ItemsService`
* `UsersService`

      /*
       * Assume that equals uses the == optimization when appropriate, and that
       * it would check hash codes as an optimization when appropriate. If we
       * did these things, it would just make things worse for the most
       * performance-conscious users.
       */
      if (key.equals(candidateKey)) {
        return entry.getValue();
      }
    }
    return null;
  }

You can also use `response_model=None` to disable creating a response model for that *path operation*, you might need to do it if you are adding type annotations for things that are not valid Pydantic fields, you will see an example of that in one of the sections below.

## Return the same input data { #return-the-same-input-data }