Here's one way to go about it using lastvote time with Steem Python. You could probably go deeper by checking last comment as well but think lastvote is a good determinant of an active user.

import sys
import time
import datetime
from steem import Steem
from steem.account import Account
now=datetime.datetime.utcnow() 
my_nodes = ['https://rpc.buildteam.io','https://rpc.steemliberator.com','https://steemd.minnowsupportproject.org']
steem = Steem(my_nodes)
account = Account('money-dreamer',steem)
lastvote = account['last_vote_time']
dt=datetime.datetime.strptime(lastvote, "%Y-%m-%dT%H:%M:%S")
dif=now-dt
if dif.days < 3:
    <execute script block>

Please, excuse the lack of comments but am glad to answer any questions.