python中指定fasta文件中碱基每行以指定数目输出

[root@PC1 test2]# cat a.fa                  ## 测试fasta文件
>chr1
aattccgggttgggcccyujjjttt
ddeeeegghggii
>chr2
8883dsfdkkkfftteeessskkk
aaadddfffgggcccgggt33
ddggee
[root@PC1 test2]# cat test.py              ## 测试程序
#!/usr/bin/env python
# -*- coding: utf-8 -*-

in_file = open("a.fa", "r")

dict1 = dict()
for i in in_file:
        i = i.strip()
        if i[0] == ">":
                key = i
                dict1[key] = ""
        else:
                dict1[key] += i

for i,j in dict1.items():
        print(i)
        while(len(j) > 10):
                print(j[:10])
                j = j[10:]
        if len(j) != 0:
                print(j)

[root@PC1 test2]# python test.py           ## 执行程序
>chr1
aattccgggt
tgggcccyuj
jjtttddeee
egghggii
>chr2
8883dsfdkk
kfftteeess
skkkaaaddd
fffgggcccg
ggt33ddgge
e