do not modify the License. You may add Your own attribution
          notices within Derivative Works that You distribute, alongside
          or as an addendum to the NOTICE text from the Work, provided
          that such additional attribution notices cannot be construed
          as modifying the License.

      You may add Your own copyright statement to Your modifications and

### Use cases: external service { #use-cases-external-service }

An example could be that you have an external authentication provider that you need to call.

You send it a token and it returns an authenticated user.

This provider might be charging you per request, and calling it might take some extra time than if you had a fixed mock user for tests.

{* ../../docs_src/custom_response/tutorial009_py39.py hl[2,10] *}

You can also use the `response_class` parameter:

{* ../../docs_src/custom_response/tutorial009b_py39.py hl[2,8,10] *}

In this case, you can return the file path directly from your *path operation* function.

## Custom response class { #custom-response-class }

You can create your own custom response class, inheriting from `Response` and using it.

          do not modify the License. You may add Your own attribution
          notices within Derivative Works that You distribute, alongside
          or as an addendum to the NOTICE text from the Work, provided
          that such additional attribution notices cannot be construed
          as modifying the License.

      You may add Your own copyright statement to Your modifications and

          do not modify the License. You may add Your own attribution
          notices within Derivative Works that You distribute, alongside
          or as an addendum to the NOTICE text from the Work, provided
          that such additional attribution notices cannot be construed
          as modifying the License.

      You may add Your own copyright statement to Your modifications and

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.

///

If you have an old FastAPI app with Pydantic v1, here I'll show you how to migrate it to Pydantic v2, and the **features in FastAPI 0.119.0** to help you with a gradual migration.

## Official Guide { #official-guide }

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# 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 }

#!/usr/bin/env/python

import boto3
from botocore.client import Config

s3 = boto3.client('s3',
        endpoint_url='http://localhost:9000',
        aws_access_key_id='YOUR-ACCESSKEYID',
        aws_secret_access_key='YOUR-SECRETACCESSKEY',
        config=Config(signature_version='s3v4'),
        region_name='us-east-1')


def _add_header(request, **kwargs):
    request.headers.add_header('x-minio-extract', 'true')

With **FastAPI** you get all of **Pydantic**'s features (as FastAPI is based on Pydantic for all the data handling):

* **No brainfuck**:
    * No new schema definition micro-language to learn.
    * If you know Python types you know how to use Pydantic.