首先我是初学者，没有找到类似于linux sed替换命令的方法，主要逻辑是读取文件，清空文件，将修改之后的内容再写进去。这种方法问题很多，例如同时操作文件或者文件过大。这只是一种方法。
全文修改：
[admin@pe-jira python]$ cat ming.txt
qqqqqqqqqq:qqqqqqqq:0
99999999999:123456789:0
111:111:11111111
>>> f = open('ming.txt','r+')
>>> a = f.readlines()
>>> f = open('ming.txt','w')
>>> for i in a:
... f.write(i.replace('wangxu','--------------'))
...
22
17
26
27
>>> f.close()
>>>
[admin@pe-jira python]$ cat ming.txt
qqqqqqqqqq:qqqqqqqq:0
111:111:11111111
--------------:222:222222
--------------01:333:33333
修改指定行
[admin@pe-jira python]$ cat ming.txt
1:111:111
1:22222:222
3:33333:222
>>> f = open('ming.txt','r')
>>> a = f.readlines()
>>> f = open('ming.txt','w')
>>> for i in a:
... f.write(i.replace('1:111:111','9:999:999'))
...
10
12
12
>>> f.close()
>>>
[admin@pe-jira python]$ cat ming.txt
9:999:999
1:22222:222
3:33333:222
re正则全文替换
[admin@pe-jira python]$ cat ming.txt
9:999:9998
3:33333:2
0:999:99999
>>> f = open('ming.txt','r')
>>> a = f.read()
>>> import re
>>> s = re.sub(r"999",'--------',a)
>>> f = open('ming.txt','w')
>>> f.write(s)
53
>>> s
'9:--------:--------8\n3:33333:2\n0:--------:--------99\n'
>>> f.close()
>>> [admin@pe-jira python]$ cat ming.txt
9:--------:--------8
3:33333:2
0:--------:--------99
[admin@pe-jira python]$
re正则只替换第一个匹配的
[admin@pe-jira python]$ cat ming.txt
9:999:9998
3:33333:2
0:999:99999
>>> f = open('ming.txt','r')
>>> a = f.read()
>>> import re
>>> s = re.sub(r"999",'--------',a,1)
>>> f = open('ming.txt','w')
>>> f.write(s)
38
>>> f.close()
>>>
[admin@pe-jira python]$ cat ming.txt
9:--------:9998
3:33333:2
0:999:99999
[admin@pe-jira python]$