[ python-Bugs-1396471 ] file.tell() returns illegal value on Windows

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Bugs item #1396471, was opened at 2006-01-04 02:53
Message generated for change (Settings changed) made by birkenfeld
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Category: Windows
Group: Python 2.4
Status: Open
Resolution: None
>Priority: 7
Submitted By: Tom Goddard (tom_goddard)
Assigned to: Nobody/Anonymous (nobody)
Summary: file.tell() returns illegal value on Windows

Initial Comment:
The file tell() method returns an illegal value that causes an exception 
when passed to seek().  This happens on Windows when a file that 
contains unix-style newlines '\n' is opened and read in text mode 'r'.  
Below is code that produces the problem on Windows 2.4.2 in an IDLE 
shell.

The bug does not occur when using mode 'rU' or 'rb'.  But I expect 
correct behaviour with mode 'r'.  My understanding is that 'rU' 
translates line endings to '\n' in the returned string while mode 'r' still 
correctly reads the lines using readline(), recognizing all 3 common 
endline conventions, but does not translate (ie includes \n\r or \r or \n 
in returned string).

The error in the tell() return value depends on how long the file is.  
Changing the 'more\n'*10 line in the example code will cause different 
incorrect return values.

Previous bug reports have mentioned problems with tell/seek when 
using file iterators, the file.next() method and the "for line in file:" 
construct.  This bug is different and just involves readline() and tell() 
with mode 'r'.

Example code tellbug.py follows:

wf = open('testdata', 'wb')
wf.write('01234\n56789\n'+ 'more\n'*10)
wf.close()

f = open('testdata', 'r')
f.readline()
t = f.tell()
print t
f.seek(t)

-------

Running gives:

>>> execfile('tellbug.py')
-5

Traceback (most recent call last):
  File "<pyshell#14>", line 1, in -toplevel-
    execfile('tellbug.py')
  File "tellbug.py", line 9, in -toplevel-
    f.seek(t)
IOError: [Errno 22] Invalid argument

----------------------------------------------------------------------

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