Handle out of scale value

[hrbonz]

Handle negative and out of scale values.

Add an option to force out of scale calculation

[brettowe]

while doing some experiments with a air sensor in a room for smokers I played with the data and got the following error trying to convert the high PM numbers the PM10 number was 566.8 as you can see below in the trace and error I believe this is exactly what this bug mentions

Traceback (most recent call last): File "./aqi-test.py", line 24, in (aqi.POLLUTANT_PM10, row[5]), File "/usr/lib/python2.7/site-packages/aqi/init.py", line 45, in to_aqi return _aqi.aqi(ccs) File "/usr/lib/python2.7/site-packages/aqi/algos/base.py", line 36, in aqi _iaqi = self.iaqi(elem, cc) File "/usr/lib/python2.7/site-packages/aqi/algos/base.py", line 78, in iaqi (aqilo, aqihi) = self.piecewise['aqi'][idx] IndexError: list index out of range list index out of range error with row: (u'2017-09-17 17:55:00', 269.8, 514.2, 173.9, 297.3, 566.8, 191.8)

[allairgoo]

Now with fire in Australia Ozone and PM value go too high

File "/home/rva/.local/lib/python3.6/site-packages/aqi/init.py", line 45, in to_aqi return _aqi.aqi(ccs) File "/home/rva/.local/lib/python3.6/site-packages/aqi/algos/base.py", line 36, in aqi _iaqi = self.iaqi(elem, cc) File "/home/rva/.local/lib/python3.6/site-packages/aqi/algos/base.py", line 91, in iaqi (aqilo, aqihi) = self.piecewise['aqi'][idx] IndexError: list index out of range

[hrbonz]

Fundamentally, the correct behavior would be to raise an exception that qualifies the value as out of AQI calculation range.

[tomasz-lewicki]

Hey @hrbonz How about returning float('inf') if the pollutant value is above the maximum threshold? That should be backward-compatible in most cases and will have predictable behavior in numerical comparisons.