for my code

Code:
for orf in [mydna[start.start():end.start()+3] for start in re.finditer('(?=ATG)',mydna
           for end in re.finditer('(?=TAA|TAG|TGA)',mydna if end.start()>start.start() and (end.end()-start.start())%3 == 0]:
        #print orf
How to make the program stop at the first end regions .