Python Dewpoint from Temperature and Humidty, Celcius

dewpoint.py

#!/usr/bin/env python

import math

def dewpoint(r,T):
    if(T<=0):
        raise ValueError('Algorithm not suitable for the given temperature')
    return (b * (math.log( (r/100)*6.1078*(10**((a*T)/(b+T))) /6.1078,10) ) / 
            (a - (math.log( (r/100)*6.1078*(10**((a*T)/(b+T))) /6.1078,10) )))

# Relative humidity, 0-100 %
relhum = 50

# Temperature in Degree Celcius, only > 0
temp = 20

print("Dewpoint: " + str(round(dewpoint(relhum,temp),1)) + "° Celcius")