Avoid linear search for emeter realtime and emeter_today (#622)

* Avoid linear search for emeter realtime and emeter_today

Most of the time the data we want is at the end of the
list so we now search backwards to avoid having to
scale all the data and throw most of it away

* more tweaks

* coverage

* coverage

* preen

* coverage

* branch cover

kasa/modules/usage.py

@@ -10,8 +10,9 @@ class Usage(Module):
 
     def query(self):
         """Return the base query."""
-        year = datetime.now().year
-        month = datetime.now().month
+        now = datetime.now()
+        year = now.year
+        month = now.month
 
         req = self.query_for_command("get_realtime")
         req = merge(
@@ -40,21 +41,21 @@ class Usage(Module):
     def usage_today(self):
         """Return today's usage in minutes."""
         today = datetime.now().day
-        converted = [x["time"] for x in self.daily_data if x["day"] == today]
-        if not converted:
-            return None
-
-        return converted.pop()
+        # Traverse the list in reverse order to find the latest entry.
+        for entry in reversed(self.daily_data):
+            if entry["day"] == today:
+                return entry["time"]
+        return None
 
     @property
     def usage_this_month(self):
         """Return usage in this month in minutes."""
         this_month = datetime.now().month
-        converted = [x["time"] for x in self.monthly_data if x["month"] == this_month]
-        if not converted:
-            return None
-
-        return converted.pop()
+        # Traverse the list in reverse order to find the latest entry.
+        for entry in reversed(self.monthly_data):
+            if entry["month"] == this_month:
+                return entry["time"]
+        return None
 
     async def get_raw_daystat(self, *, year=None, month=None) -> Dict:
         """Return raw daily stats for the given year & month."""