最强悍的从文件的最后行开始读取行数，谁能解释一下这条语句？

firmlyjin

1.     def tail(f, n, offset=None):
   
2.         """Reads an lines from f with an offset of offset lines. The return value is a tuple
   
3.         in the form ``(lines, has_more)`` where `has_more` is an indicator that is `True`
   
4.         if there are more lines in the file. """
   
5.         avg_line_length = 74
   
6.         to_read = n + (offset or 0)
   
7.         while 1:
   
8.             try: f.seek(-(avg_line_length * to_read), 2)
   
9.             except IOError: # woops. apparently file is smaller than what we want # to step back, go to the beginning instead
   
10.                 f.seek(0)
    
11.             pos = f.tell()
    
12.             lines = f.read().splitlines() #分行
    
13.             if len(lines) >= to_read or pos == 0:
    
14.                 return lines[-to_read:offset and -offset or None],len(lines) > to_read or pos > 0
    
15.             avg_line_length *= 1.3
    

复制代码

return lines[-to_readffset and -offset or None],len(lines) > to_read or pos > 0

谁能解释一下上面这条语句？

firmlyjin

sorry，我既然不知道元组的定义方法

>>> c = 1,2
>>> c
(1, 2)

>>>lst = []
>>> lst[1:True and True or None]
[]