字串替換可以用內建的方法和正則表示式完成。
1用字串本身的replace方法:

a = 'hello word'
b = a.replace('word','python')
print b

例子：

#encoding=utf-8
# Created by double lin at 2018/8/7
# 獲取小說“花千骨”
import urllib2
import re

if __name__ == '__main__':
    url = 'http://www.136book.com/huaqiangu/'
    head = {}
    head['User-Agent'] = 'Mozilla/5.0 (Linux; Android 4.1.1; Nexus 7 Build/JRO03D) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.166  Safari/535.19'
    req = urllib2.Request(url, headers=head)
    response = urllib2.urlopen(req)
    html = response.read()
    # print html
    url_name = re.findall(r'<li><a href="(.+?)">(.+?)</a></li>', html, re.S)
    f = open('hello.txt', 'w')
    for i in range(len(url_name)):
        print url_name[i][0],
        print url_name[i][1]
        url = url_name[i][0]
        name = url_name[i][1]
        if url != '\n':
            req = urllib2.Request(url,headers=head)
            r =urllib2.urlopen(req)
            # print r.read()
            html1 = r.read()
            content = re.findall(r'<br /><p>(.+?)</p><br />', html1, re.S)
            for i in range(len(content)):
                # print type(content[i])
                f.write(name+'\n\n')
                content[i] = content[i].replace('</p><p>', '\n')
                # print content[i]
                f.write(content[i]+'\n\n')
    f.close()
 

2用正則表示式來完成替換:

import re
a = 'hello word'
strinfo = re.compile('word')
b = strinfo.sub('python',a)
print b