How to set jEPlus parameter with Python?

edit

I am currently working on jEPlus 2.0 and I need to set a parameter (P1) which depends on the value of another parameter (P2) by an IF clause.

The script is very simple, if pv type (P1) is "Mono", the pv price (P2) is gonna be 65 while if the type is "Poly" the price is 48. I am able to get the values of P1 from jEPlus (using sys.argv), however I do not understand how to "send back" the value from python to jEPlus, so that @@P2@@ in the .idf takes that value.

I wonder if there is any specific function to do that (I checked on .sys guide but could not find).

Thank you very much for your help.