Make dew point optional in usaheatindex calculation

Signed-off-by: Jim Easterbrook <jim@jim-easterbrook.me.uk>

src/pywws/__init__.py

@@ -1,3 +1,3 @@
 __version__ = '18.8.0'
-_release = '1620'
-_commit = '6eb7960'
+_release = '1621'
+_commit = '61dabbb'

src/pywws/conversions.py

@@ -209,7 +209,7 @@ def cadhumidex(temp, humidity):
                            float(humidity) / 100.0)
     return temp + (0.555 * (saturation_pressure - 10.0))
 
-def usaheatindex(temp, humidity, dew):
+def usaheatindex(temp, humidity, dew=None):
     """Calculate Heat Index as per USA National Weather Service Standards
 
     See http://en.wikipedia.org/wiki/Heat_index, formula 1. The
@@ -218,6 +218,8 @@ def usaheatindex(temp, humidity, dew):
     """
     if temp is None or humidity is None:
         return None
+    if dew is None:
+        dew = dew_point(temp, humidity)
     if temp < 26.7 or humidity < 40 or dew < 12.0:
         return temp
     T = (temp * 1.8) + 32.0

src/pywws/service/weathercloud.py

@@ -66,8 +66,8 @@ class ToService(pywws.service.LiveDataService):
 #temp_out                                                   "'temp'     : '%.1f',"#
 #calc "wind_chill(data['temp_out'], data['wind_ave'])"      "'chill'    : '%.1f',"#
 #calc "dew_point(data['temp_out'], data['hum_out'])"        "'dew'      : '%.1f',"#
-#calc "usaheatindex(data['temp_out'], data['hum_out'], dew_point(data['temp_out'], data['hum_out']))" "'heat' : '%.1f',"#
-#calc "(usaheatindex(data['temp_out'], data['hum_out'], dew_point(data['temp_out'], data['hum_out'])) - (1.072 * wind_mph(data['wind_ave']))) " "'thw' : '%.1f',"#
+#calc "usaheatindex(data['temp_out'], data['hum_out'])" "'heat' : '%.1f',"#
+#calc "(usaheatindex(data['temp_out'], data['hum_out']) - (1.072 * wind_mph(data['wind_ave'])))" "'thw' : '%.1f',"#
 #hum_out                                                    "'hum'      : '%.d',"#
 #wind_ave                                                   "'wspdavg'  : '%.1f',"#
 #wind_gust                                                  "'wspdhi'   : '%.1f',"#
@@ -91,7 +91,7 @@ def __init__(self, context, check_params=True):
 #temp_in  "'tempin': '%.1f',"#
 #hum_in   "'humin' : '%.d',"#
 #calc "dew_point(data['temp_in'], data['hum_in'])"          "'dewin'    : '%.1f',"#
-#calc "usaheatindex(data['temp_in'], data['hum_in'], dew_point(data['temp_in'], data['hum_in']))" "'heatin' : '%.1f',"#
+#calc "usaheatindex(data['temp_in'], data['hum_in'])" "'heatin' : '%.1f',"#
 """
 
     @contextmanager