Python修改文本指定行

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]$