Issue 4633: file.tell() gives wrong result (original) (raw)

I find that file.tell returns not the byte offset of the next byte, but possibly the byte offset of the next block to be read. I find it always to be a multiple of 1024. Following is a demo of the bug. where I read a few lines into a text file, step back by the length of the last read line, read again, and do not find the same data. What is returned is the tail part of a line way down in the file. I woeked around by keeping track of the file pointer, and seek worked fine. tell() is at fault. ----------demonstration on a text file Python 2.5.1 (r251:54863, Nov 14 2007, 16:00:54) [GCC 3.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information.

jf=open('junk','r') line=jf.next() line '\n' line=jf.next() line 'See COPYING file in the same directory as this one for license.\n' line=jf.next() line '\n' line=jf.next() line 'Thank you for trying this utility. I had great fun putting it\n' line=jf.next() line 'together, and I hope users will find it useful.\n' jf.seek(len(line),1) line=jf.next() line 'gle says Maps will not work without it. file:// URLs are \n'

O.K. But, is there a way to backtrack to the beginning of the last read line, without explicitly implementing accounting of the real file pointer in the code, and doing "seek(,0)"?

The documentation you pointed to implies that, in "for name in file:" loop a clean backtracking is not possible. Am I missing something?

Thanks.