Flag control variable

[luke.geelen at gmail.com]

hello,
i'd like to know how to set up a flag to change a variable,
for example, i want a simple script to combine 2 numbers,


sum = num + another_num
print "Now the sum of the numbers equals : ", sum

how could i make it so that if i type python ./script.py 21 41 
that i get the sum of 21 and 41 ?

luke