They are more relevant for older versions, before OpenAPI 3.1.0 was available.

You can consider this a brief OpenAPI and JSON Schema **history lesson**. 🤓

///

/// warning

These are very technical details about the standards **JSON Schema** and **OpenAPI**.

## About Pydantic { #about-pydantic }

Pydantic includes the tests for **FastAPI** with its own tests, so new versions of Pydantic (above `1.0.0`) are always compatible with FastAPI.

You can pin Pydantic to any version above `1.0.0` that works for you.

For example:

```txt
pydantic>=2.7.0,<3.0.0

/// info

The parameter `summary` is available in OpenAPI 3.1.0 and above, supported by FastAPI 0.99.0 and above.

///

## Overriding the defaults { #overriding-the-defaults }

Using the information above, you can use the same utility function to generate the OpenAPI schema and override each part that you need.

async with lifespan(app):
    await do_stuff()
```

When you create a context manager or an async context manager like above, what it does is that, before entering the `with` block, it will execute the code before the `yield`, and after exiting the `with` block, it will execute the code after the `yield`.

In our code example above, we don't use it directly, but we pass it to FastAPI for it to use it.

/// warning

The Pydantic team stopped support for Pydantic v1 for the latest versions of Python, starting with **Python 3.14**.

This includes `pydantic.v1`, which is no longer supported in Python 3.14 and above.

If you want to use the latest features of Python, you will need to make sure you use Pydantic v2.

///

/// info

Webhooks are available in OpenAPI 3.1.0 and above, supported by FastAPI `0.99.0` and above.

///

## An app with webhooks { #an-app-with-webhooks }

    // enclosing, exterior
    assertEquals(range, range.intersection(Range.closed(2, 10)));

    // overlap above
    assertEquals(Range.closed(6, 8), range.intersection(Range.closed(6, 10)));

    // adjacent above
    assertEquals(Range.openClosed(8, 8), range.intersection(Range.openClosed(8, 10)));

    // separate above
    expected =
        assertThrows(

This is still supported thanks to **Pydantic**, as it has [internal support for `dataclasses`](https://docs.pydantic.dev/latest/concepts/dataclasses/#use-of-stdlib-dataclasses-with-basemodel).

So, even with the code above that doesn't use Pydantic explicitly, FastAPI is using Pydantic to convert those standard dataclasses to Pydantic's own flavor of dataclasses.

And of course, it supports the same:

* data validation
* data serialization

    // enclosing, exterior
    assertEquals(range, range.intersection(Range.closed(2, 10)));

    // overlap above
    assertEquals(Range.closed(6, 8), range.intersection(Range.closed(6, 10)));

    // adjacent above
    assertEquals(Range.openClosed(8, 8), range.intersection(Range.openClosed(8, 10)));

    // separate above
    expected =
        assertThrows(

{* ../../docs_src/stream_data/tutorial001_py310.py ln[44:47] hl[47] *}

## A Custom `PNGStreamingResponse` { #a-custom-pngstreamingresponse }

In the examples above, the data bytes were streamed, but the response didn't have a `Content-Type` header, so the client didn't know what type of data it was receiving.