[ python-Bugs-1521491 ] file.seek() influelce write() when opened with a+ mode

[SourceForge.net]

Bugs item #1521491, was opened at 2006-07-12 22:04
Message generated for change (Comment added) made by rudnik_lior
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1521491&group_id=5470

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
not just the latest update.
Category: Python Interpreter Core
Group: Python 2.5
>Status: Open
Resolution: None
Priority: 5
Submitted By: Lior (rudnik_lior)
Assigned to: Nobody/Anonymous (nobody)
Summary: file.seek() influelce write() when opened with a+ mode

Initial Comment:
Python 2.5b1 (r25b1:47027, Jun 20 2006, 09:31:33)

Assuming documentation is correct: (from seek() help
"Note that if the file is opened for appending (mode
'a' or 'a+'), any seek() operations will be undone at
the next write"

Doing the following is __not__ undoing the seek
operation after calling this a few times (Simplified
code snippet):

from __future__ import with_statement
with open(path,'a+') as f:
    f.seek(0,2) # go to end
    pos = f.tell() 
    f.seek(0,0)
    line = f.readline().strip()
    f.seek(0,2) # go to end, not effective if opened
with mode a/a+ (currently bug?)
    f.write("something")

Calling the above code repeatedly didnt increase the
file size beyond 166 bytes (in my code)



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

>Comment By: Lior (rudnik_lior)
Date: 2006-07-28 13:35

Message:
Logged In: YES 
user_id=1364480

This issue is on windows XP.
Wasnt tested on other versions (only 2.5b1 and b2)

I expect the code to always write at the end according to
the documentation. However if I user file seek (opend as A+)
to read from begining of the file, the write also goes to
begining of file.

Note - in the code snippet, please remove the last
f.seek(0,2) to see the problem! (it should have been in a
comment)

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

Comment By: Georg Brandl (gbrandl)
Date: 2006-07-13 07:43

Message:
Logged In: YES 
user_id=849994

I also cannot see any problem with the above code and can
append to a file indefinitely. What exactly are you
expecting the code to do, and what do you get? Which OS is this?

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

Comment By: Neal Norwitz (nnorwitz)
Date: 2006-07-13 06:29

Message:
Logged In: YES 
user_id=33168

This seems to work for me on Linux.  Maybe we are testing
differently.  What o/s and version are you using?  Does this
work with Python 2.4?  Can you attach a complete test case
that demonstrates this problem?

Thanks.

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

Comment By: Lior (rudnik_lior)
Date: 2006-07-12 22:09

Message:
Logged In: YES 
user_id=1364480

Re-tried the code with empty file - it doesnt grow beyond
creating and writting at position 0 so it seems the seek
does influence the write position.

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

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1521491&group_id=5470