get_dew_point raises unhandled ValueError with negative humidity

[rwx]

kolson@rwx:~$ /opt/extras.ubuntu.com/my-weather-indicator/bin/my-weather-indicator
/home/kolson
<gettext.GNUTranslations instance at 0x1930290>
No LSB modules are available.
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Distributor ID: Ubuntu
Description: Ubuntu 12.04.2 LTS
Release: 12.04
Codename: precise
Version: x86_64
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My-Weather-Indicator version: 0.6.1.2.precise.1
#####################################################
('/home/kolson/.config/my-weather-indicator/my-weather-indicator.conf', True)
{"time":"2013-04-16 08:42","countryName":"United States","sunset":"2013-04-16 19:40","rawOffset":-7,"dstOffset":-6,"countryCode":"US","gmtOffset":-7,"lng":-105.084423,"sunrise":"2013-04-16 06:20","timezoneId":"America/Denver","lat":40.5852602}
SE
(<type 'str'>, u'26 \xb0F')
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mwi-wind12.png
start now
East
(<type 'str'>, u'26 \xb0F')
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mwi-wind00.png
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(<type 'str'>, u'26 \xb0F')
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mwi-wind12.png
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(<type 'str'>, u'31 \xb0F')
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(<type 'str'>, u'32 \xb0F')
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Traceback (most recent call last):
  File "/opt/extras.ubuntu.com/my-weather-indicator/share/my-weather-indicator/myweatherindicator.py", line 196, in work
    self.set_menu()
  File "/opt/extras.ubuntu.com/my-weather-indicator/share/my-weather-indicator/myweatherindicator.py", line 464, in set_menu
    weather = self.weatherservice1.get_weather()
  File "/opt/extras.ubuntu.com/my-weather-indicator/share/my-weather-indicator/wundergroundapi.py", line 148, in get_weather
    weather_data = self._get_weather()
  File "/opt/extras.ubuntu.com/my-weather-indicator/share/my-weather-indicator/wundergroundapi.py", line 101, in _get_weather
    weather_data['current_conditions']['dew_point'] = weatherservice.get_dew_point(humidity,temperature,self.units.temperature)
  File "/opt/extras.ubuntu.com/my-weather-indicator/share/my-weather-indicator/weatherservice.py", line 457, in get_dew_point
    dp = math.pow(h/100.0,1.0/8.0)*(110.0+t) - 110.0
ValueError: math domain error

[rwx (karl-olson)]

I believe the only possible cause for this is when h is negative. I have no idea how this changes the dew point calculation, but with the following change I have been running without error for 24 hours now:

  dp = math.pow(math.fabs(h)/100.0,1.0/8.0)*(110.0+t) - 110.0

[rwx (karl-olson)]

With the above fix in place, I now occasionally see that humidity is being reported as -999%.

[Cas (calumlind)]

-999% suggests an error in feed data and you cannot have negative humidity so simply test that h > 0 before attempting calculation, and if not let it return 'n/a'