[Python-Dev] os.rename on windows

[Raghuram Devarakonda]

Hi,

I have submitted a patch (http://www.python.org/sf/1704547) that
allows os.rename to replace the destination file if it exists, on
windows. As part of discussion in the tracker, Martin suggested that
python-dev should discuss the change.

Currently, os.rename() on windows uses the API MoveFile() which fails
if the destination file exists. The patch replaces this API with
MoveFileEx() and uses the flag MOVEFILE_REPLACE_EXISTING which causes
the destination file to be replaced if it exists. However, this change
is subtle and if there is any existing code that depends on current
os.rename behaviour on windows, their code is silently broken with
(any) destination file being overwritten. But the functionality of
replacing is important and I would like to know the best of way of
supporting it. If it is deemed that this change is not good to go in
as-is, how about having an optional parameter to os.rename (say,
win_replace) that can be used by callers to explicitly request
replacing?

I must also point out that the patch uses another flag
MOVEFILE_COPY_ALLOWED effectively allowing renamed files to be on
separate file systems. The renaming in this case is not atomic and I
used this flag only to support current functionality. It is not a bad
idea to disallow such renames which brings it in line with the
behaviour on many unix flavors. This also has the potential to break
code but not silently.

Lastly, I found an old discussion about the same topic by this list.

http://mail.python.org/pipermail/python-dev/2001-May/014957.html

Even though Guido indicated that he doesn't support API change in this
thread, I am posting again as I did not see any one mention
MoveFileEx() in that thread.

Thanks,
Raghu.