!!! 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}.

            if new_translation_message in comment.body:
                already_notified_comment = comment
            elif done_translation_message in comment.body:
                already_done_comment = comment
        logging.info(
            f"Already notified comment: {already_notified_comment}, already done comment: {already_done_comment}"
        )

        if pr.state == "open" and awaiting_label in label_strs:

# Development - Contributing

First, you might want to see the basic ways to [help FastAPI and get help](help-fastapi.md){.internal-link target=_blank}.

## Developing

If you already cloned the <a href="https://github.com/tiangolo/fastapi" class="external-link" target="_blank">fastapi repository</a> and you want to deep dive in the code, here are some guidelines to set up your environment.

### Virtual environment with `venv`

  - name: Feature Request
    about: To suggest an idea or ask about a feature, please start with a question saying what you would like to achieve. There might be a way to do it already.
    url: https://github.com/tiangolo/fastapi/discussions/categories/questions
  - name: Show and tell
    about: Show what you built with FastAPI or to be used with FastAPI.

    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=409, detail="Item already exists")
    fake_db[item.id] = item

            "title": "The Foo ID Stealers",
            "description": "There goes my stealer",
        },
    )
    assert response.status_code == 400

# About FastAPI versions

**FastAPI** is already being used in production in many applications and systems. And the test coverage is kept at 100%. But its development is still moving quickly.

New features are added frequently, bugs are fixed regularly, and the code is still continuously improving.

Then I found that there was a standard to document APIs, using JSON (or YAML, an extension of JSON) called Swagger.

And there was a web user interface for Swagger APIs already created. So, being able to generate Swagger documentation for an API would allow using this web user interface automatically.

At some point, Swagger was given to the Linux Foundation, to be renamed OpenAPI.

You can try it already in the interactive docs:

<img src="/img/tutorial/security/image03.png">

We are not verifying the validity of the token yet, but that's a start already.

## Recap

    field: ModelField,
    *,
    cloned_types: Optional[MutableMapping[Type[BaseModel], Type[BaseModel]]] = None,
) -> ModelField:
    if PYDANTIC_V2:
        return field
    # cloned_types caches already cloned types to support recursive models and improve
    # performance by avoiding unnecessary cloning
    if cloned_types is None:
        cloned_types = _CLONED_TYPES_CACHE

    original_type = field.type_