请问用python如何进行替换啊？

Question

请问用python如何进行替换啊？
在Ubuntu下使用Python
将a.txt中所有（aaa）替换为

Answer 1

import os

dir_list = ['./src1','./src2']
rows_dict = dict()
rows_dict['aaa'] = 'bbb' 

for dir_name in dir_list:
    for file_name in os.listdir(dir_name):
        if os.path.isdir(dir_name + os.path.sep + file_name):
            continue

        with open(dir_name + os.path.sep + file_name, 'r') as fr:
            content = fr.read()

        for k, v in rows_dict.iteritems():
            content = content.replace(k, v)

        with open(dir_name + os.path.sep + file_name, 'w') as fw:
            fw.write(content)