Reading a text file backwards

[Jay]

I have a very large text file (being read by a CGI script on a web server),
and I get memory errors when I try to read the whole file into a list of
strings. The problem is, I want to read the file backwards, starting with
the last line.

Previously, I did:

myfile = open('myfile.txt', 'r')
mylines = myfile.readlines()
myfile.close()
for line in range(len(mylines)-1, -1, -1):
    # do something with mylines[line]

This, however caused a "MemoryError," so I want to do something like

myfile = open('myfile.txt', 'r')
for line in myfile:
    # do something with line
myfile.close()

Only, I want to iterate backwards, starting with the last line of the file.
Can anybody suggest a simple way of doing this? Do I need to jump around
with myfile.seek() and use myfile.readline() ?