Python论坛的帖子：

Thu Dec 29 09:28:42 HKT 2005

fsock = file(filename, 'rU')

你这个U参数是什么作用啊？查了一下，说是：
Add a 'U' to mode to open the file for input with universal newline
不明白什么意思，

还有
'U' cannot be combined with 'w' or '+' mode.
为什么？
没用过，请教。

-----邮件原件-----
发件人: python-chinese-bounces at lists.python.cn [mailto:python-chinese-bounces at lists.python.cn] 代表 Kevin Yuan
发送时间: 2005年12月28日 16:18
收件人: python-chinese at lists.python.cn
主题: 垃圾邮件:Re: [python-chinese] 读取超大文件的最后一行或者多行

#last lines
def last_lines(filename, lines = 1):
    #print the last several line(s) of a text file
    """
    Argument filename is the name of the file to print.
    Argument lines is the number of lines to print from last. 
    """
    block_size = 1024
    block = ''
    nl_count = 0
    start = 0
    fsock = file(filename, 'rU')
    try:
        #seek to end
        fsock.seek(0, 2)
        #get seek position 
        curpos = fsock.tell()
        while(curpos > 0): #while not BOF
            #seek ahead block_size+the length of last read block
            curpos -= (block_size + len(block));
            if curpos < 0: curpos = 0 
            fsock.seek(curpos)
            #read to end
            block = fsock.read()
            nl_count = block.count('\n')
            #if read enough(more)
            if nl_count >= lines: break 
        #get the exact start position
        for n in range(nl_count-lines+1):
            start = block.find('\n', start)+1 
    finally:        
        fsock.close()
    #print it out  
    print block[start:] 

if __name__ == '__main__':
    import sys
    last_lines(sys.argv[0], 5) #print the last 5 lines of THIS file
在05-12-28，Vincent Wen < vincentwen at gmail.com> 写道：
python 也可以seek啊，seek到文件尾，然后从后往前找回车符 

在 05-12-27，hoxide Ma<hoxide at gmail.com> 写道：
> 用mmap
>
> 在 05-12-27，bu shehui<bushehui at gmail.com> 写道：
> > If you use Linux, you can use the command such as
> >
> >           tail -n 1  #the last  line
> >
> >
> > good luck
> >
> > 2005-12-27
> > 
> >
> >
> > On 12/22/05, Weigang LI <dimens at gmail.com> wrote:
> > >
> > >
> > > 各位好，
> > > 请问用什么样的方法读取一个超大文件的最后一行，或者文件末尾的n行。 
> > > 由于文件非常大，顺序读取非常的耗时，怎样实现效率高？
> > >
> > > 谢谢。
> > > _______________________________________________
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标题：答复: 垃圾邮件:Re: [python-chinese] 读取超大文件的最后一行或者多行