Question on sorting

[Lad]

Hi,
I have a file of records of 4 fields each.
Each field is separated by a semicolon. That is

Filed1;Ffield2;Field3;Field4

But there may be also empty records such as
;;;;
(only semicolons).

For sorting I used
#################
lines = file('Config.txt').readlines()# a file I want to sort
lines.sort()
ff=open('ConfigSorted.txt','w')# sorted file
ff.writelines(lines)
ff.close()
###############
It was sorted but empty records were first. I need them to be last(at
the end of the file). How can I do that?

Thanks for help
Lad