[Python-Dev] Why do we flush before truncating?

[Neil Schemenauer]

On Sat, Sep 06, 2003 at 01:11:14PM -0400, Tim Peters wrote:
> I don't understand why we're flushing the file.  ftruncate() isn't a
> standard C function, so the standard sheds no light on why we might be doing
> that.

The fflush call as been there forever. The truncate method was added
in 2.36 by Guido.  I think the code was actually from Jim Roskind:

  http://groups.google.com/groups?selm=199412070213.SAA06932%40infoseek.com

He says:

  Note that since the underlying ftruncate operates on a file
  descriptor (believe it or not), it was necessary to fflush() the
  stream before performing the truncate.  I thought about doing a
  seek() as well, but could not find compelling reason to move the
  stream pointer.

That still gives me no clue as to why the fflush() was deemed
necessary.  I found this posting:

  http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=35E0DB62.1BDD2D30%40taraz.kz&rnum=1

but, AFACK, the reason the program is not working the way the poster
expects is the missing fflush() call before the lseek() call (not
the fflush() before the ftruncate()).

  Neil