backreferences

[Amy Dillavou]

Can someone help me with understanding how python uses backreferences?
I need to remember the item that was last matched by the re engine but i
cant seem to understand anything that I find on backreferences.  if I
want to access the last match do i use \number or is there something
else i have to do?

heres part of my code:
renDate = re.compile("$((\d){4}-(\d){2}-(\d){2}))")
renDate.search(l)
if(exist.search(l) and str(lastmodDate) < \1): #i need help here with \1

Thanks in advance
A.D