[Python-Dev] os.rename() behavior

[Gustavo Niemeyer]

Hello folks,

I've just been asked by Thomas Waldmann (moin maintainer) about the
rename() behavior in Linux (posix) vs.  Windows. Here is the function
documentation:

  rename(src, dst)

  Rename the file or directory src to dst. If dst is a directory,
  OSError will be raised. On Unix, if dst exists and is a file, it will
  be removed silently if the user has permission. The operation may fail
  on some Unix flavors if src and dst are on different filesystems. If
  successful, the renaming will be an atomic operation (this is a POSIX
  requirement). On Windows, if dst already exists, OSError will be
  raised even if it is a file; there may be no way to implement an
  atomic rename when dst names an existing file. Availability:
  Macintosh, Unix, Windows.


While I understand that this is an operating system behavior, and the os
module is meant to hold incompatible functionality, I do belive that
most of us developing in posix systems have never checked if a rename
failed because the file already exists. IOW, this will usually be
discovered when the program blows up for the first time in Windows
(that's how Thomas discovered).

Is it too late to implement the forced rename internally, and leave the
programmer test it with os.path.exists() if he really wants to?

I know this will cause incompatibilities in programs which expect the
current behavior. OTOH, programs that expect this behavior are already
broken in any posix system.

What do you think?

-- 
Gustavo Niemeyer
http://niemeyer.net