Frappe date functions

Hi,

i want to add new doc with 1 expiry column that automatically set 3 month after posting date
i wonder how i can do this

is there any fucntion to do this?

Try using python dateutil and relativedelta

can you give an example ?..
i have no idea how to use it without example or furhter explanation about the param and the return

Thanks

https://www.google.co.in/search?q=python+dateutil+relativedelta&ie=utf-8&oe=utf-8&gws_rd=cr&ei=FuvzVMXuL9GeugSO5ILQDQ#q=python+add+days+to+date

ohhh isee…so have to use python code because there is no frappe method for this…
thanks