ha-core/CONTRIBUTING.md

# Adding support for a new device

For help on building your component, please see the [developer documentation](https://home-assistant.io/developers/) on [home-assistant.io](https://home-assistant.io/).

After you finish adding support for your device:

 - update the supported devices in README.md.
 - add any new dependencies to requirements.txt.
 - Make sure all your code passes Pylint, flake8 (PEP8 and some more) validation. To generate reports, run `pylint homeassistant > pylint.txt` and `flake8 homeassistant --exclude bower_components,external > flake8.txt`.

If you've added a component:

 - update the file [`domain-icon.html`](https://github.com/balloob/home-assistant/blob/master/homeassistant/components/http/www_static/polymer/domain-icon.html) with an icon for your domain ([pick from this list](https://www.polymer-project.org/0.5/components/core-elements/demo.html#core-icon))
 - update the demo component with two states that it provides
 - Add your component to home-assistant.conf.example

Since you've updated domain-icon.html, you've made changes to the frontend:

 - run `build_frontend`. This will build a new version of the frontend. Make sure you add the changed files `frontend.py` and `frontend.html` to the commit.

## Setting states

It is the responsibility of the component to maintain the states of the devices in your domain. Each device should be a single state and, if possible, a group should be provided that tracks the combined state of the devices.

A state can have several attributes that will help the frontend in displaying your state:

 - `friendly_name`: this name will be used as the name of the device
 - `entity_picture`: this picture will be shown instead of the domain icon
 - `unit_of_measurement`: this will be appended to the state in the interface
 - `hidden`: This is a suggestion to the frontend on if the state should be hidden

These attributes are defined in [homeassistant.components](https://github.com/balloob/home-assistant/blob/master/homeassistant/components/__init__.py#L25).

## Proper Visibility Handling ##

Generally, when creating a new entity for Home Assistant you will want it to be a class that inherits the [homeassistant.helpers.entity.Entity](https://github.com/balloob/home-assistant/blob/master/homeassistant/helpers/entity.py) Class. If this is done, visibility will be handled for you. 
You can set a suggestion for your entity's visibility by setting the hidden property by doing something similar to the following.

```python
self.hidden = True
```

This will SUGGEST that the active frontend hides the entity. This requires that the active frontend support hidden cards (the default frontend does) and that the value of hidden be included in your attributes dictionary (see above). The Entity abstract class will take care of this for you.

Remember: The suggestion set by your component's code will always be overwritten by user settings in the configuration.yaml file. This is why you may set hidden to be False, but the property may remain True (or vice-versa).

## Working on the frontend

The frontend is composed of Polymer web-components and compiled into the file `frontend.html`. During development you do not want to work with the compiled version but with the seperate files. To have Home Assistant serve the seperate files, set `development=1` for the http-component in your config.

When you are done with development and ready to commit your changes, run `build_frontend`, set `development=0` in your config and validate that everything still works.

## Notes on PyLint and PEP8 validation

In case a PyLint warning cannot be avoided, add a comment to disable the PyLint check for that line. This can be done using the format `# pylint: disable=YOUR-ERROR-NAME`. Example of an unavoidable PyLint warning is if you do not use the passed in datetime if you're listening for time change.