upsert and preserve existing values?

gistfile1.py

for itm in itms:
  data = itm
  rec=coll.find({'text':data})
  if rec.count() == 0:
    print "new item: {0}".format(itm.strip())
    coll.insert({'text':data,'count':0,'last_posted': OLD_DATE})


can the coll.find/coll.insert be rewritten to use upsert (coll.update) **and preserve any existing values of count(integer) and last_posted(date)**?

each document in the collection will be text, count, last_posted .

text: some arbitrary text
count: an incremented count
last_posted: a date, initialized to an date in 1900.