# Header Parameter Models

If you have a group of related **header parameters**, you can create a **Pydantic model** to declare them.

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

## Header Parameters with a Pydantic Model

# Templating - `Jinja2Templates`

You can use the `Jinja2Templates` class to render Jinja templates.

Read more about it in the [FastAPI docs for Templates](https://fastapi.tiangolo.com/advanced/templates/).

You can import it directly from `fastapi.templating`:

```python
from fastapi.templating import Jinja2Templates
```

/*
 * Copyright 2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

  - type: textarea
    attributes:
      label: API(s)
      description: Which existing classes or methods do you want to improve?
      placeholder: e.g., `com.google.common.collect.ImmutableList::of`
      render: java
    validations:
      required: true

  - type: textarea
    attributes:
      label: How do you want it to be improved?
    validations:
      required: true

  - type: textarea
    attributes:

    validations:
      required: true
  - type: textarea
    id: go-env
    attributes:
      label: "Output of `go env` in your module/workspace:"
      render: shell
    validations:
      required: true
  - type: textarea
    id: what-did-you-do
    attributes:
      label: "What did you do?"

# Server Workers - Uvicorn with Workers

Let's check back those deployment concepts from before:

* Security - HTTPS
* Running on startup
* Restarts
* **Replication (the number of processes running)**
* Memory
* Previous steps before starting

Up to this point, with all the tutorials in the docs, you have probably been running a **server program**, for example, using the `fastapi` command, that runs Uvicorn, running a **single process**.

/*
 * Copyright 2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

// has been used.
// The returned reader contains the payload.
func waitForHTTPResponse(respBody io.Reader) (io.Reader, error) {
	reader := bufio.NewReader(respBody)
	for {
		b, err := reader.ReadByte()
		if err != nil {
			return nil, err
		}
		// Check if we have a response ready or a filler byte.
		switch b {
		case 0:
			return reader, nil
		case 1:
			errorText, err := io.ReadAll(reader)

///

## Parâmetros do Cabeçalho com um Modelo Pydantic

Declare os **parâmetros de cabeçalho** que você precisa em um **modelo do Pydantic**, e então declare o parâmetro como `Header`:

//// tab | Python 3.10+

```Python hl_lines="9-14  18"
{!> ../../docs_src/header_param_models/tutorial001_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="9-14  18"

app.dependency_overrides = {}
```

/// tip | "Tipp"

Wenn Sie eine Abhängigkeit nur während einiger Tests überschreiben möchten, können Sie die Überschreibung zu Beginn des Tests (innerhalb der Testfunktion) festlegen und am Ende (am Ende der Testfunktion) zurücksetzen.