Logged In: YES 
user_id=33168

I don't see any problems with the new code.  One nit though,
I hate using l as a variable name because it's difficult to
tell if it's an l (ell) or a 1 (one).  I realize O_cwrite
uses l.  I'm not against n though. :-)

Should the docstring be updated?  It says the parameter is a
sequence_of_strings.  I'm not sure if it would be good to call
it an iterable_of_strings.  That sounds funny.

I think it's good that it takes an iterable.  That makes it
more like
StringIO.

Should StringIO.writelines() be changed?  It currently does:
 self.write(''.join(list))