import notmuch

db = notmuch.Database(mode=notmuch.Database.MODE.READ_WRITE)

query_str = "tag:this_is_my_test"

query1 = notmuch.Query(db, query_str)

for msg in query1.search_messages():
    msg.freeze()
    print "At start tags are %s" % ", ".join(msg.get_tags())
    msg.add_tag("added_first")
    query2 = notmuch.Query(db, query_str)
    for msg2 in query2.search_messages():
        msg2.freeze()
        msg2.add_tag("added_second")
        msg2.thaw()
        print "Inside inner loop tags are %s" % ", ".join(msg2.get_tags())
    msg.thaw()
    print "At end tags are %s" % ", ".join(msg.get_tags())
    msg.remove_tag("added_first")