question on subprogram parameter

[skyworld]

Hi,

I'm studying python now and I saw a piece of code like this:

def storeDbase(db, dbfilename=dbfilename):
     .....
     dbfile=open(dbfilename,'w')
     for key in db:
          print(key, file=dbfile)


can anybody help me to understand what does this "file=dbfile" mean
and what is its function? thanks.