Allow specifying a data source input

[atopuzov]

• Allows creation of dashboards which parametrise the input datasource [1]

Python code

...
dashboard = Dashboard(
    inputs=[
        DataSourceInput(
            name="DS_PROMETHEUS",
            type="datasource",
            label="Prometheus",
            pluginId="prometheus",
            pluginName="Prometheus"
        )],
...

Generated JSON

...
  "__inputs": [
    {
      "description": "",
      "label": "Prometheus",
      "name": "DS_PROMETHEUS",
      "pluginId": "prometheus",
      "pluginName": "Prometheus",
      "type": "datasource"
    }
  ],
...

Python code

...
    inputs=[
        ConstantInput(
            name="VAR_PREFIX",
            label="prefix",
            value="collectd"
        ),
...

Generated JSON

...
  "__inputs": [
    {
      "description": "",
      "label": "prefix",
      "name": "VAR_PREFIX",
      "type": "constant",
      "value": "collectd"
    },
...

[1] http://docs.grafana.org/reference/export_import/

[jml]

Thanks!

This seems pretty useful, but I'm a bit wary of introducing inheritance into grafanalib. We've managed to avoid it so far and I think that's for the best.

Do you have ideas about how we could do this without it?

[atopuzov]

It is only 2 attributes, so no much duplication. Also attr lib did not play well with inheritance (eg. description had to be copied as it has a default).

I'll just remove inheritance and push the change.

[atopuzov]

@jml Pushed the changes without inheritance

[jml]

Great, thanks!