为什么写了换行语句，结果还是没有换行？

Question

想把文件冒号后面的数字，按照每行写入另一个文件，在每行末尾换行，用以下代码，有换行语句，结果还是没换行，怎么办？

#!/usr/bin/python
#coding:utf-8
import pickle
import re
tfidf_dict={}
tfidf_all=[]
with open('/home/user1/zhouchun/lda/KNN/single_tfidf.txt','a') as file:
with open('/home/user1/zhouchun/lda/KNN/train_tfidf.txt', 'r') as fw:
        # content = fw.readlines()
        for line in fw:
            index_tfidf=line.split()
            # print index_tfidf
            for j in index_tfidf:
                m=re.compile(r'^(\d+):(\d+)$')
                try:
                    word_index=m.match(j).group(1)
                    tfidf=m.match(j).group(2)
                    file.write(str(tfidf) + ' ')
                except:
                     word_index=None
                     tfidf=None
        file.write('\n')

Answer 1

windows上换行应该为\r\n. 所以file.write('\r\n').

Answer 2

缩进不对。

Answer 3

with open('a.txt', 'r') as f1, open('b.txt', 'a') as f2:
    for line in f1:
        new_line = [_.split(':')[1] for _ in line.split()]
        f2.write(' '.join(new_line))
        f2.write('\n')