Pandas : SQL SelfJoin With Date Criteria

One query I often do in SQL within a relational database is to join a table back to itself and summarize each row based on records for the same id either backwards or forward in time.

For example, assume table1 as columns 'ID','Date', 'Var1'

In SQL I could sum var1 for the past 3 months for each record like this:

Select a.ID, a.Date, sum(b.Var1) as sum_var1
from table1 a
left outer join table1 b
on a.ID = b.ID
and months_between(a.date,b.date) <0
and months_between(a.date,b.date) > -3

Is there any way to do this in Pandas?

from Pandas : SQL SelfJoin With Date Criteria