def f1(seq):
    seen = set()
    return [ x for x in seq if x not in seen and not seen.add(x)]
    
def f7(seq):
    seen = set()
    seen_add = seen.add
    return [ x for x in seq if x not in seen and not seen_add(x)]
    
import dis
print "f1"
dis.dis(f1)

print "f7"
dis.dis(f7)