How to modify configuration file with Python

Question

I am trying to modify a configuration file using Python. How can I do the equivalent of multiple sed commands in this format:

sed -ci 's/ServerTokens OS/ServerTokens Prod/' /etc/httpd/conf/httpd.conf

most efficiently in Python? This is what I am doing right now:

with open("httpd.conf", "r+") as file:
    tmp = []
    for i in file:
        if '#ServerName' in i:
            tmp.append(i.replace('#ServerName www.example.com', 'ServerName %s' % server_name , 1))
        elif 'ServerAdmin' in i:
            tmp.append(i.replace('root@localhost', webmaster_email, 1))
        elif 'ServerTokens' in i:
            tmp.append(i.replace('OS', 'Prod', 1))
        elif 'ServerSignature' in i:
            tmp.append(i.replace('On', 'Off', 1))
        elif 'KeepAlive' in i:
            tmp.append(i.replace('Off', 'On', 1))
        elif 'Options' in i:
            tmp.append(i.replace('Indexes FollowSymLinks', 'FollowSymLinks', 1))
        elif 'DirectoryIndex' in i:
            tmp.append(i.replace('index.html index.html.var', 'index.php index.html', 1))
        else:
            tmp.append(i)
    file.seek(0)
    for i in tmp:
        file.write(i)

It's needlessly complex since I could just use subprocess and sed instead. Any suggestions?

Funny. Are you bound to use python if you can do it alternatively? — devnull
– devnull, Commented Apr 3, 2014 at 11:06
Pythons equivilant of sed: docs.python.org/2/library/re.html#re.sub — Torxed
– Torxed, Commented Apr 3, 2014 at 11:13
Use python config parser, i.e. docs.python.org/2/library/configparser.html. Makes things easier! — schmi
– schmi, Commented Apr 3, 2014 at 11:57
@PythonNoob: the docs say right there, "Lines beginning with '#' or ';' are ignored and may be used to provide comments." — John Zwinck
– John Zwinck, Commented Apr 3, 2014 at 15:43

Krzysztof Adamski · Accepted Answer · 2014-04-25 07:15:43Z

1

You can use regular expressions inside of Python in very similar way you do this in sed. Just use Python regular expressions library. You may be interested in re.sub() method, which does equivalent of sed's s command used in your example.

If you want to do this efficiently, you probably have to run only one substitute command per line, skipping it if it was changed, similar way you do this in your example code. In order to achieve that, you may use re.subn instead of re.sub or re.match combined with groups that were matched.

Here's an example:

import re

server_name = 'blah'
webmaster_email = '[email protected]'

SUBS = ( (r'^#ServerName www.example.com', 'ServerName %s' % server_name),
        (r'^ServerAdmin root@localhost', 'ServerAdmin %s' % webmaster_email),
        (r'KeepAlive On', 'KeepAlive Off')
       )

with open("httpd.conf", "r+") as file:
    tmp=[]
    for i in file:
        for s in SUBS:
            ret=re.subn(s[0], s[1], i)
            if ret[1]>0:
                tmp.append(ret[0])
                break
        else:
            tmp.append(i)
    for i in tmp:
        print i,

edited Apr 25, 2014 at 7:15

answered Apr 6, 2014 at 17:03

Krzysztof Adamski

2,09911 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Python Novice Over a year ago

care to share an example with re.sub or resubn? It's confusing me

Collectives™ on Stack Overflow

How to modify configuration file with Python

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related