Python If missing value in list do this else print

I have this currently

def missing(frames):
if len(m) >= 1:
    m.append(str((list(chain.from_iterable((frames[i] + d for d in xrange(1, diff))
        for i, diff in enumerate(imap(sub, frames[1:], frames))
        if diff > 1)))))
return m
else:
    print 'no frames are missing'

How would I make an if statement to say if there are no missing frames print no missing frames in the flag? My current program doesnt work at all. It only appends frames if they are missing it doesnt print out no frames are missing