Allow conversion from date strings to "unix" timestamp. (#1985)

"unix" timestamp is number of seconds since Jan 1, 1970 UTC.
This allows scripts that use templates to generate time
deltas in seconds if desired from state attributes such
as last_updated.

Some examples:

timestamp now is
{{ as_timestamp(now) }}

timstamp of last change is
{{ as_timestamp(states.binary_sensor.garage_door.last_changed) }}

seconds since last change is
{{ as_timestamp(now) - as_timestamp(states.binary_sensor.garage_door.last_changed) }}

homeassistant/helpers/template.py

@@ -56,6 +56,7 @@ def render(hass, template, variables=None, **kwargs):
             'now': dt_util.as_local(utcnow),
             'states': AllStates(hass),
             'utcnow': utcnow,
+            'as_timestamp': dt_util.as_timestamp,
         }).render(kwargs).strip()
     except jinja2.TemplateError as err:
         raise TemplateError(err)

homeassistant/util/dt.py

@@ -1,4 +1,5 @@
 """Provides helper methods to handle the time in HA."""
+import calendar
 import datetime as dt
 import re
 
@@ -59,6 +60,17 @@ def as_utc(dattim):
     return dattim.astimezone(UTC)
 
 
+def as_timestamp(dt_value):
+    """Convert a date/time into a unix time (seconds since 1970)."""
+    if hasattr(dt_value, "utctimetuple"):
+        parsed_dt = dt_value
+    else:
+        parsed_dt = parse_datetime(str(dt_value))
+        if not parsed_dt:
+            raise ValueError("not a valid date/time.")
+    return calendar.timegm(parsed_dt.utctimetuple())
+
+
 def as_local(dattim):
     """Convert a UTC datetime object to local time zone."""
     if dattim.tzinfo == DEFAULT_TIME_ZONE:

tests/util/test_dt.py

@@ -107,6 +107,19 @@ class TestDateUtil(unittest.TestCase):
             datetime(1986, 7, 9, tzinfo=dt_util.UTC),
             dt_util.utc_from_timestamp(521251200))
 
+    def test_as_timestamp(self):
+        """Test as_timestamp method."""
+        ts = 1462401234
+        utc_dt = dt_util.utc_from_timestamp(ts)
+        self.assertEqual(ts, dt_util.as_timestamp(utc_dt))
+        utc_iso = utc_dt.isoformat()
+        self.assertEqual(ts, dt_util.as_timestamp(utc_iso))
+
+        # confirm the ability to handle a string passed in
+        delta = dt_util.as_timestamp("2016-01-01 12:12:12")
+        delta -= dt_util.as_timestamp("2016-01-01 12:12:11")
+        self.assertEquals(1, delta)
+
     def test_parse_datetime_converts_correctly(self):
         """Test parse_datetime converts strings."""
         assert \