ダイレクトメッセージを送れるかどうかで判断するみたいなつぶやきが流れてたので。
setでごにょれば良かろうと。
import twitter
api = twitter.Api(username='user',password='pass')
friends = set([u.name for u in api.GetFriends()])
followers = set([u.name for u in api.GetFollowers()])
print "follow and followed: " + ",".join(list(friends.intersection(followers)))
print "not follow but followed: " + ",".join(list(followers.difference(friends)))
print "follow but not followed: " + ",".join(list(friends.difference(followers)))