Removing last line while appending to file

[Tim Wegener]

Hi, 

Is there a simple way to remove the last line (or arbitrary trailing
portion) of a file, when appending to it? 

I want to write a log file in xml, which requires root elements around
all the log data. This means that when I want to append to the log I
must first remove the trailing </log> element. 

I have tried using file.seek() and file.tell() to no avail. I would
prefer not to parse the entire file each time I want to simply append an
entry. 

Thanks, 
Tim