Python模块应用 (linecache)

Posted 2020-08-04 ops

linecache是专门支持读取大文件，而且支持行式读取的函数库。 linecache 预先把文件读入缓存起来，后面如果你访问该文件的话就不再从硬盘读取。对于大文件的读取效率还不错

Help on module linecache:

NAME
    linecache - Cache lines from files.

FILE
    /usr/local/lib/python2.7/linecache.py

MODULE DOCS
    http://docs.python.org/library/linecache

DESCRIPTION
    This is intended to read lines from modules imported -- hence if a filename
    is not found, it will look down the module search path for a file by
    that name.

FUNCTIONS
    checkcache(filename=None)
        Discard cache entries that are out of date.
        (This is not checked upon each call!)
    
    clearcache()
        Clear the cache entirely.
    
    getline(filename, lineno, module_globals=None)

DATA
    __all__ = [\'getline\', \'clearcache\', \'checkcache\']

help(linecache)

常用的方法：

linecache.getlines(filename,)  #接收一个文件对象，返回一个列表，列表中的每个元素就是文件中的一行. 和readlines()一样
linecache.getline(filename,lineno)  #接收一个文件对象和一个行数，返回指定行数对应的行内容

>>> linecache.getlines(\'/etc/passwd\')
[\'root:x:0:0:root:/root:/bin/bash\\n\', \'bin:x:1:1:bin:/bin:/sbin/nologin\\n\', \'daemon:x:2:2:daemon:/sbin:/sbin/nologin\\n\', \'adm:x:3:4:adm:/var/adm:/sbin/nologin\\n\', \'lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin\\n\', \'sync:x:5:0:sync:/sbin:/bin/sync\\n\', \'shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown\\n\', \'halt:x:7:0:halt:/sbin:/sbin/halt\\n\', \'mail:x:8:12:mail:/var/spool/mail:/sbin/nologin\\n\', \'uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin\\n\', \'operator:x:11:0:operator:/root:/sbin/nologin\\n\', \'games:x:12:100:games:/usr/games:/sbin/nologin\\n\', \'gopher:x:13:30:gopher:/var/gopher:/sbin/nologin\\n\', \'ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin\\n\', \'nobody:x:99:99:Nobody:/:/sbin/nologin\\n\', \'dbus:x:81:81:System message bus:/:/sbin/nologin\\n\', \'vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin\\n\', \'abrt:x:173:173::/etc/abrt:/sbin/nologin\\n\', \'haldaemon:x:68:68:HAL daemon:/:/sbin/nologin\\n\', \'ntp:x:38:38::/etc/ntp:/sbin/nologin\\n\', \'saslauth:x:499:76:"Saslauthd user":/var/empty/saslauth:/sbin/nologin\\n\', \'postfix:x:89:89::/var/spool/postfix:/sbin/nologin\\n\', \'sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin\\n\', \'tcpdump:x:72:72::/:/sbin/nologin\\n\', \'ansibletest:x:500:500::/home/ansibletest:/bin/bash\\n\', \'mysql:x:27:27:MySQL Server:/var/lib/mysql:/bin/bash\\n\', \'zabbix:x:498:499:Zabbix Monitoring System:/var/lib/zabbix:/sbin/nologin\\n\', \'apache:x:48:48:Apache:/var/www:/sbin/nologin\\n\', \'elasticsearch:x:497:498:elasticsearch user:/home/elasticsearch:/sbin/nologin\\n\', \'redis:x:496:497:Redis Server:/var/lib/redis:/sbin/nologin\\n\', \'pythons:x:501:501::/home/pythons:/bin/bash\\n\']

linecache.getlines() 

>>> linecache.getline(\'/etc/passwd\',10)
\'uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin\\n\'
>>> linecache.getline(\'/etc/passwd\',5)
\'lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin\\n\'

linecache.getline()