FAQ
I'm the one responsible for SET_LINENO going away in 2.3, so here's
my take...

Bruce Dawson <bruce_deletethis_dawson at cygnus-software.com> writes:
Executive summary: Has the SET_LINENO removal been tested with the HAP
debugger,
No. I'd never heard of it for one thing!
and wouldn't a breakpoint instruction give much larger
benefits?
I fail to see how.
As a partial author of the HAP Python Debugger (available on source
forge) I read about the imminent removal of SET_LINENO with some
worry. It *sounds* like it has been done in such way to not cause
debugger problems, but I'm curious if anyone has tested HAP with 2.3.
I tried really hard to make it transparent to debuggers. There are a
few very small differences, but unless you're actually scanning for
SET_LINENO instructions they shouldn't bite. I'd invite you to test,
of course.
Also, it sounds like the reason for removing SET_LINENO was to improve
the performance of Python scripts. However one of the posts on this
topic (can't find it now) suggested that the hoped for improvements
had not actually materialized.
It speeds programs run without -O. On Windows, programs run with -O
got somewhat slower after this patch (on Linux it made essentially no
difference, maybe a very slight speedup). See Tim's post.
It seems to me (from the sidelines/peanut gallery/wherever) that the
biggest performance problems in the SET_LINENO area are when
debugging, not when running free, and that therefore this optimization
is targeting the lesser problem.
You've got my motivation entirely backwards there.
The need to check for breakpoints at each line has always made Python
debugging performance poor at best. Technically the performance under
the debugger doesn't matter, and yet sometimes it does. Having just
helped complete a Python based sports game for PC, where real-time
performance was critical, I can say that the slowdown in HAP was
definitely annoying.
You're faced with a hard problem. Good luck :)
So, wouldn't a break-point opcode be a more substantial improvement
than removing SET_LINENO? Just bringing up that old topic again to see
if it gets any more traction :-)
How would a breakpoint opcode differ from what SET_LINENO was?
P.S. For reference I include the canonical? link to the SET_LINENO
discussion.

http://mail.python.org/pipermail/python-dev/2000-July/007652.html
Note that what I did bears little resemblance to the scheme sketched
in that post. I hack stuff out of co_lnotab.
P.P.S. A breakpoint instruction would also be a boon for asserts - I'd
love to be able to stop on the assert when running under a debugger,
to see what is wrong before the stack frame unwinds.
Well, you break on the exception, don't you?

Cheers,
M.

--
The "of course, while I have no problem with this at all, it's
surely too much for a lesser being" flavor of argument always
rings hollow to me. -- Tim Peters, 29 Apr 1998

Search Discussions

Discussion Posts

Previous

Follow ups

Related Discussions

Discussion Navigation
viewthread | post
posts ‹ prev | 7 of 8 | next ›
Discussion Overview
grouppython-list @
categoriespython
postedSep 26, '02 at 6:09a
activeSep 27, '02 at 10:37a
posts8
users6
websitepython.org

People

Translate

site design / logo © 2022 Grokbase