Using file objects with elementtree

[dj]

Hello,

Rather then holding my XML document in memory before writing it to
disk, I want to create a file object that elementtree will write each
element to has it is created. Does any one know how to do that ?

Here is my code so, far:

fd = open("page.xml", "w")
tree.write( fd, encoding="iso-8859-1")

I know there's something I am doing wrong, but I just do not know
what.