http://learnpythonthehardway.org/book/凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字凑字