Question

In the book – Core Python Programming, there is following example –

>>> f = open('/tmp/x', 'w+')
>>> f.tell()
0
>>> f.write('test line 1\n')  # add 12-char string [0-11]
>>> f.tell()
12
>>> f.write('test line 2\n')  # add 12-char string [12-23]
>>> f.tell()                  # tell us current file location (end))
24

When I run the same code in my interpreter, I get 13L in place of 12 and 26L in place of 24.
I am running python 2.5 on Windows.

Has anything changed regarding behaviour or tell() in versions? How does tell decide the position in the file.

Thanks and Regards

Answer 1

Your file is opened in text mode. In that mode Python on Windows makes a translation between Windows line-endings and Unix line endings. On Windows a line ending is two characters while on Unix it is one ('\n'), hence your result is expected.

If you open the file in binary mode, you don’t get these translations.

f = open('/tmp/x', 'wb+')

And you would get 12 and 24 back from tell() as well.