In this case, you could want to document how that external API *should* look like. What *path operation* it should have, what body it should expect, what response it should return, etc.

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

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

)

// SHA256Mismatch - when content sha256 does not match with what was sent from client.
type SHA256Mismatch struct {
	ExpectedSHA256   string
	CalculatedSHA256 string
}

func (e SHA256Mismatch) Error() string {
	return "Bad sha256: Expected " + e.ExpectedSHA256 + " does not match calculated " + e.CalculatedSHA256
}

// BadDigest - Content-MD5 you specified did not match what we received.
type BadDigest struct {
	ExpectedMD5   string

Follow your cloud provider's guides to deploy FastAPI apps with them. 🤓

## Deploy your own server { #deploy-your-own-server }

---
name: Feature request
about: Suggest an idea
title: ''
labels: enhancement
assignees: ''

---

Start by telling us what problem you’re trying to solve. Often a solution already exists!

    validations:
      required: true

  - type: textarea
    attributes:
      label: Expected Behavior
      description: What did you expect to happen?
    validations:
      required: true

  - type: textarea
    attributes:
      label: Actual Behavior
      description: What actually happened?
    validations:
      required: true

  - type: dropdown
    attributes:
      label: Packages

projects: ["golang/29"]
body:
- type: textarea
  attributes:
    label: Summary
    description: >
      What change are you proposing to the upload configuration, and why?
      For new upload configuration, which new counters will be collected, what
      do they measure, and why is it important to collect them?
      Note that uploaded data must not carry sensitive user information.

### FastAPI Data Filtering { #fastapi-data-filtering }

Now, for FastAPI, it will see the return type and make sure that what you return includes **only** the fields that are declared in the type.

## What is a Container Image { #what-is-a-container-image }

A **container** is run from a **container image**.

  - type: textarea
    id: context
    attributes:
      label: Context
      description: |
        How has this issue affected you? What are you trying to accomplish? What other alternatives have you considered?
        Providing context helps us come up with a solution that is most useful in the real world
    validations:

## Context Managers { #context-managers }

### What are "Context Managers" { #what-are-context-managers }

"Context Managers" are any of those Python objects that you can use in a `with` statement.