# Yaml

## Introduction

The Yaml Extension includes the [`YamlOutputHandler`](http://cement.readthedocs.io/en/3.0/api/ext/ext_yaml/#cement.ext.ext_yaml.YamlOutputHandler) to render output in pure Yaml, as well as the [`YamlConfigHandler`](http://cement.readthedocs.io/en/3.0/api/ext/ext_yaml/#cement.ext.ext_yaml.YamlConfigHandler) that allows applications to use Yaml configuration files as a drop-in replacement of the default [`ConfigParserConfigHandler`](https://cement.readthedocs.io/en/3.0/api/ext/ext_configparser/#cement.ext.ext_configparser.ConfigParserConfigHandler).

**Documentation References:**

* [Configuration Settings](/core-foundation/configuration-settings.md)
* [Output Rendering](/core-foundation/output-rendering.md)

**API References:**

* [Cement Yaml Extension](https://cement.readthedocs.io/en/3.0/api/ext/ext_yaml/)
* [Yaml Library](https://pyyaml.org/wiki/PyYAMLDocumentation)

## Requirements

* pyYaml

{% hint style="info" %}
Cement 3.0.8+:

`pip install cement[yaml]`
{% endhint %}

{% hint style="warning" %}
Applications using Cement <3.0.8 should continue to include `pyYaml` in their dependencies.
{% endhint %}

## Configuration

This extension does not support any application level configuration settings or meta options.

## Usage

### Config Handler

{% tabs %}
{% tab title="Example: Using Yaml Config Handler" %}
{% code title="myapp.py" %}

```python
from cement import App

class MyApp(App):
    class Meta:
        label = 'myapp'
        extensions = ['yaml']
        config_handler = 'yaml'
        config_file_suffix = '.yml'
```

{% endcode %}

{% code title="\~/.myapp.yml" %}

```
---
myapp:
    foo: bar
```

{% endcode %}
{% endtab %}
{% endtabs %}

### Output Handler

In general, you likely would not set `output_handler` to `yaml`, but rather another type of output handler that displays readable output to the end-user (ex: Mustache, Jinja2, or Tabulate). However, Cement supports overriding handlers via command line options if the [`Handler.Meta.overridable`](http://cement.readthedocs.io/en/3.0/api/core/handler/#cement.core.handler.Handler.Meta.overridable) option is set. For example, `-o yaml` will trigger the framework to use the `yaml` output handler, overriding the default set in [`App.Meta.output_handler`](http://cement.readthedocs.io/en/3.0/api/core/foundation/#cement.core.foundation.App.Meta.output_handler).

See the documentation on [Overriding Handlers via Command Line](/core-foundation/interfaces-and-handlers.md#overriding-handlers-via-command-line).

{% tabs %}
{% tab title="Example: Using Yaml Output Handler" %}
{% code title="myapp.py" %}

```python
from cement import App, init_defaults

META = init_defaults('output.yaml')
META['output.yaml']['overridable'] = True

class MyApp(App):
    class Meta:
        label = 'myapp'
        extensions = ['yaml', 'mustache']
        meta_defaults = META
        output_handler = 'mustache'
        template_dir = './templates'

with MyApp() as app:
    app.run()
    data = {'foo': 'bar'}
    app.render(data, 'example.m')
```

{% endcode %}

{% code title="templates/example.m" %}

```
Foo: {{ foo }}
```

{% endcode %}
{% endtab %}

{% tab title="cli" %}

```
$ python myapp.py
Foo: bar

$ python myapp.py -o yaml
{foo: bar}
```

{% endtab %}
{% endtabs %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.builtoncement.com/extensions/yaml.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.