[Python-Dev] cpython (2.7): #9559: Append data to single-file mailbox files if messages are only added

[Petri Lehtinen]

Antoine Pitrou wrote:
> > If messages were only added, a new file is no longer created and
> > renamed over the old file when flush() is called on an mbox, MMDF or
> > Babyl mailbox.
> 
> Why so? Appending is not atomic and, if it fails in the middle, you
> could get a corrupt mbox file.
> Furthermore, I disagree that it's a bugfix: IMO it should wait for 3.4.

The code previosly already appended messages to the end of the file
when calling add(). This patch just changed it to not do a full
rewrite when flush() is called. Having a partially written message in
the end of your mailbox doesn't seem like a fatal corruption to me.

Furthermore, I (and R. David Murray) think this is not so surprising
for users. Most (or all) other implementations always write changes
in-place without renaming, as this makes it possible to find out
whether new mail has arrived.