{* ../../docs_src/pydantic_v1_in_v2/tutorial002_an_py310.py hl[2,5,15] *}

/// warning

Have in mind that as the Pydantic team no longer supports Pydantic v1 in recent versions of Python, starting from Python 3.14, using `pydantic.v1` is also not supported in Python 3.14 and above.

///

///

The files will be uploaded as "form data".

If you declare the type of your *path operation function* parameter as `bytes`, **FastAPI** will read the file for you and you will receive the contents as `bytes`.

Keep in mind that this means that the whole contents will be stored in memory. This will work well for small files.

But there are several cases in which you might benefit from using `UploadFile`.

Passing the `root_path` to `FastAPI` would be the equivalent of passing the `--root-path` command line option to Uvicorn or Hypercorn.

### About `root_path` { #about-root-path }

Keep in mind that the server (Uvicorn) won't use that `root_path` for anything else than passing it to the app.

In this case, you would accept any `dict` as long as it has `int` keys with `float` values:

{* ../../docs_src/body_nested_models/tutorial009_py39.py hl[7] *}

/// tip

Keep in mind that JSON only supports `str` as keys.

But Pydantic has automatic data conversion.

For example, to declare another response with a status code `404` and a Pydantic model `Message`, you can write:

{* ../../docs_src/additional_responses/tutorial001_py39.py hl[18,22] *}

/// note

Keep in mind that you have to return the `JSONResponse` directly.

///

/// info

The `model` key is not part of OpenAPI.

```
Client #1596980209979 left the chat
```

/// tip

The app above is a minimal and simple example to demonstrate how to handle and broadcast messages to several WebSocket connections.

But keep in mind that, as everything is handled in memory, in a single list, it will only work while the process is running, and will only work with a single process.

     * final long[] will be a "rolling snapshot" of the state of the bit array. This is usually good
     * enough, but should be kept in mind.
     */
    public static long[] toPlainArray(AtomicLongArray atomicLongArray) {
      long[] array = new long[atomicLongArray.length()];
      for (int i = 0; i < array.length; ++i) {

Including how to handle lifespan state that can be used in other areas of your code.

///

## Sub Applications { #sub-applications }

Of course, there are some cases where there's no problem in running the previous steps multiple times, in that case, it's a lot easier to handle.

/// tip

Also, keep in mind that depending on your setup, in some cases you **might not even need any previous steps** before starting your application.

In that case, you wouldn't have to worry about any of this. 🤷

///

**FastAPI** provides the same `starlette.responses` as `fastapi.responses` just as a convenience for you, the developer. But most of the available responses come directly from Starlette.

///

/// warning

Have in mind that the `RequestValidationError` contains the information of the file name and line where the validation error happens so that you can show it in your logs with the relevant information if you want to.