def comp(seq):
<EOL>return seq.replace("<STR_LIT:A>", '<STR_LIT:t>').replace('<STR_LIT:T>', '<STR_LIT:a>').replace('<STR_LIT:C>', '<STR_LIT:g>').replace('<STR_LIT>', '<STR_LIT:c>').replace('<STR_LIT:n>', '<STR_LIT>').upper().replace("<STR_LIT>", "<STR_LIT:n>")<EOL>
returns a seq with complement. Preserves little n's for splitters.