Vapor Pressure Deficit Calculator

# -*- coding: utf-8 -*-
"""
Created on Sat Oct 10 18:33:00 2015

@author: nayani
"""

""" The module is used to calculate the Saturated vapor pressure, actual vapor pressure
and the vapor pressure deficit using temperature and relative humidity values.
The variales and the funstiions of the program  is defined as follows;
T=Temperature in Celsius (EX: 20 C)
RH=Relative Humidity in Percentage (35%)
getSatVapourPressure(T) #Calulate the Saturated vapor pressure using temperature
EX: A=getSatVapourPressure(20)
getvaporPressure(RH,T) # Calculate the actual vapor pressure using both temperature and the realtive humidity
EX: B=getvaporPressure(35,20)
getVPD(T,RH) # Calculate the vapor pressure deficit
EX= C=getVPD(35,20)
"""
import math
import sys
# Calculates the Saturated Vapor pressure Using temperature in Celcius Degrees. The equation only 
considers tempertures above zero Celcius. Add a if statement to consider both below zero and
above zero Celcius conditions.
def getSatVapourPressure(T):
    SVP=0.611*math.exp(17.3*T/(237.3+T))
    return SVP    
 # function to calculate the actual vapour pressure for the given temperature and humidity data   
def getvaporPressure(RH,T):
        VP=RH*getSatVapourPressure(T)
        return VP       
# function to calculate the      vapour pressure deficit
def getVPD(T,RH):
    VPDefit=getSatVapourPressure(T)-getvaporPressure(RH,T)
    return VPDefit
# test block to run the program as a module or as a program
if __name__=='__main__':
    print 'run as a program'
    print getVPD(float(sys.argv[1]),float(sys.argv[2]))