如何用python替换sed-like文本？

Question

我想启用此文件中的所有apt存储库

cat /etc/apt/sources.list
## Note, this file is written by cloud-init on first boot of an instance                                                                                                            
## modifications made here will not survive a re-bundle.                                                                                                                            
## if you wish to make changes you can:                                                                                                                                             
## a.) add 'apt_preserve_sources_list: true' to /etc/cloud/cloud.cfg                                                                                                                
##     or do the same in user-data
## b.) add sources in /etc/apt/sources.list.d                                                                                                                                       
#                                                                                                                                                                                   

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to                                                                                                           
# newer versions of the distribution.                                                                                                                                               
deb http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick main                                                                                                                   
deb-src http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick main                                                                                                               

## Major bug fix updates produced after the final release of the                                                                                                                    
## distribution.                                                                                                                                                                    
deb http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick-updates main                                                                                                           
deb-src http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick-updates main                                                                                                       

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu                                                                                                         
## team. Also, please note that software in universe WILL NOT receive any                                                                                                           
## review or updates from the Ubuntu security team.                                                                                                                                 
deb http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick universe                                                                                                               
deb-src http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick universe                                                                                                           
deb http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick-updates universe
deb-src http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
# deb http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick multiverse
# deb-src http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick multiverse
# deb http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick-updates multiverse
# deb-src http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick-backports main restricted universe multiverse
# deb-src http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ maverick-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu maverick partner
# deb-src http://archive.canonical.com/ubuntu maverick partner

deb http://security.ubuntu.com/ubuntu maverick-security main
deb-src http://security.ubuntu.com/ubuntu maverick-security main
deb http://security.ubuntu.com/ubuntu maverick-security universe
deb-src http://security.ubuntu.com/ubuntu maverick-security universe
# deb http://security.ubuntu.com/ubuntu maverick-security multiverse
# deb-src http://security.ubuntu.com/ubuntu maverick-security multiverse

有了sed，这是一个简单的sed -i 's/^# deb/deb/' /etc/apt/sources.list最优雅的（“pythonic”）方法是什么？

Answer 1

你可以这样做：

with open("/etc/apt/sources.list", "r") as sources:
    lines = sources.readlines()
with open("/etc/apt/sources.list", "w") as sources:
    for line in lines:
        sources.write(re.sub(r'^# deb', 'deb', line))

with语句确保文件正确关闭，在"w"模式下重新打开文件会在写入文件之前清空该文件。sub（pattern，replace，string）与sed/perl中的s/pattern/replace/等价。

编辑：示例中的固定语法