[Python]如何取出一個超大文字檔的最後幾行

　　這是　python-中國　郵件清單中的一個問題。如果不考慮效率問題，這個問題可能很簡單，直接read出整個檔案的內容，然後split一下或者還有更簡單的辦法。但是如果這個檔案是“超大”，那麼為了區區幾行而讀入整個檔案有點‘“得不償失“。下面是我的實現。剛學python不久，也許沒有發揮出它的優點。

#last lines
#by Kevin Yuan
def last_lines(filename, lines = 1):
    #print the last 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