Add index parameter to scrape sensor (#21084)

* Add index parameter to scrape sensor

The scrape sensor selects the first element of the list returned by
BeautifulSoup. This commit adds an optional index parameter to allow the
selection of a different element from the list of results. To make this
a non-breaking change, if no index value is configured, the sensor
defaults to the previous behaviour of returning the first element.

* Set default value for index to avoid later checks

homeassistant/components/sensor/scrape.py

@@ -26,6 +26,7 @@
 
 CONF_ATTR = 'attribute'
 CONF_SELECT = 'select'
+CONF_INDEX = 'index'
 
 DEFAULT_NAME = 'Web scrape'
 DEFAULT_VERIFY_SSL = True
@@ -34,6 +35,7 @@
     vol.Required(CONF_RESOURCE): cv.string,
     vol.Required(CONF_SELECT): cv.string,
     vol.Optional(CONF_ATTR): cv.string,
+    vol.Optional(CONF_INDEX, default=0): cv.positive_int,
     vol.Optional(CONF_AUTHENTICATION):
         vol.In([HTTP_BASIC_AUTHENTICATION, HTTP_DIGEST_AUTHENTICATION]),
     vol.Optional(CONF_HEADERS): vol.Schema({cv.string: cv.string}),
@@ -56,6 +58,7 @@ def setup_platform(hass, config, add_entities, discovery_info=None):
     verify_ssl = config.get(CONF_VERIFY_SSL)
     select = config.get(CONF_SELECT)
     attr = config.get(CONF_ATTR)
+    index = config.get(CONF_INDEX)
     unit = config.get(CONF_UNIT_OF_MEASUREMENT)
     username = config.get(CONF_USERNAME)
     password = config.get(CONF_PASSWORD)
@@ -77,19 +80,21 @@ def setup_platform(hass, config, add_entities, discovery_info=None):
         raise PlatformNotReady
 
     add_entities([
-        ScrapeSensor(rest, name, select, attr, value_template, unit)], True)
+        ScrapeSensor(rest, name, select, attr, index, value_template, unit)],
+                 True)
 
 
 class ScrapeSensor(Entity):
     """Representation of a web scrape sensor."""
 
-    def __init__(self, rest, name, select, attr, value_template, unit):
+    def __init__(self, rest, name, select, attr, index, value_template, unit):
         """Initialize a web scrape sensor."""
         self.rest = rest
         self._name = name
         self._state = None
         self._select = select
         self._attr = attr
+        self._index = index
         self._value_template = value_template
         self._unit_of_measurement = unit
 
@@ -119,9 +124,9 @@ def update(self):
 
         try:
             if self._attr is not None:
-                value = raw_data.select(self._select)[0][self._attr]
+                value = raw_data.select(self._select)[self._index][self._attr]
             else:
-                value = raw_data.select(self._select)[0].text
+                value = raw_data.select(self._select)[self._index].text
             _LOGGER.debug(value)
         except IndexError:
             _LOGGER.error("Unable to extract data from HTML")