Allow getting number of available states in template (#9158)

homeassistant/helpers/template.py

@@ -187,6 +187,10 @@ class AllStates(object):
             sorted(self._hass.states.async_all(),
                    key=lambda state: state.entity_id))
 
+    def __len__(self):
+        """Return number of states."""
+        return len(self._hass.states.async_entity_ids())
+
     def __call__(self, entity_id):
         """Return the states."""
         state = self._hass.states.get(entity_id)
@@ -213,6 +217,10 @@ class DomainStates(object):
              if state.domain == self._domain),
             key=lambda state: state.entity_id))
 
+    def __len__(self):
+        """Return number of states."""
+        return len(self._hass.states.async_entity_ids(self._domain))
+
 
 class TemplateState(State):
     """Class to represent a state object in a template."""

tests/helpers/test_template.py

@@ -782,3 +782,17 @@ def test_state_with_unit(hass):
                             hass)
 
     assert tpl.async_render() == ''
+
+
+@asyncio.coroutine
+def test_length_of_states(hass):
+    """Test fetching the length of states."""
+    hass.states.async_set('sensor.test', '23')
+    hass.states.async_set('sensor.test2', 'wow')
+    hass.states.async_set('climate.test2', 'cooling')
+
+    tpl = template.Template('{{ states | length }}', hass)
+    assert tpl.async_render() == '3'
+
+    tpl = template.Template('{{ states.sensor | length }}', hass)
+    assert tpl.async_render() == '2'