Patch 509975 fixes the conflict between gdb-mode and
python-mode by checking whether the current process is
a python process.  My patch fixes it more simply, by
only clearing the overlay arrow if we were the ones who
set it.

I'd be happy with either patch.

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I've rejected 509975 because it doesn't play nice when
you're pdb tracking from the shell (see comments in that patch).

I'm not sure this patch works correctly either, but for a
different reason: it doesn't actually work for me!

If I add "import pdb; pdb.set_trace()" to a file and then
execute the file from the shell buffer, I see the overlay
arrow.  If I then switch to a gdb debugging a C program and
hit "next", the overlay arrow in the .py buffer disappears.

This seems like a tricky problem and I don't have a good
solution, but I think I have to reject this patch too.

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The problem my patch was intended to fix is that currently
just loading python-mode.el (as happens by default under Red
Hat 7.3) breaks gdb-mode.  With my patch, it works fine.

emacs only supports one overlay arrow at a time; if you hit
'next' in gdb, gdb-mode will set the overlay arrow, which
means that it will no longer be set in the python buffer. 
This may not be ideal behavior, but it's a limitation of
emacs, not a bug in my patch.

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Hmm, it must work differently in emacs than in XEmacs (which
is what I use).  In a vanilla Emacs 21.2.1 I can't get the
overlay arrow to work even without python-mode.el loaded, so
I'll have to take your word for it.

In XEmacs, I definitely do get two overlay arrows, one in
the C buffer and one in the python-mode buffer.  As I step
through the python program, the C arrow stays nicely visible
and highlighted.  As I step through gdb though, the python
overlay arrow disappears.

Your patch makes no difference to me and I can't get overlay
arrow working at all in Emacs, so I suppose the patch is
benign.  I'll reopen it but I'd like confirmation from some
other Emacs user that this fixes the problem in that editor.
 Alternatively, maybe I should just apply it and worry about
it if people complain.

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This patch is now tracked in the python-mode project, at

http://sourceforge.net/tracker/index.php?func=detail&aid=785816&group_id=86916&atid=581351