[Python-Dev] about line numbers

Christian Tismer tismer@appliedbiometrics.com
Sat, 21 Aug 1999 23:23:10 +0200

Vladimir Marangozov wrote:
> Chris, could you please repeat that step by step in more detail?
> I'm not sure I understand your suggestions.

I think I was too quick. I thought of copying the whole
code object, of course.

> > I'd rather keep the original code object as it is, create a copy
> > with inserted breakpoints and put that into the frame slot.
> You seem to suggest to duplicate the entire code object, right?
> And reference the modified duplicata from the current frame?


> I actually duplicate only the opcode string (that is, the co_code string
> object) and I don't see the point of duplicating the entire code object.
> Keeping a reference from the current frame makes sense, but won't it
> deallocate the modified version on every frame release (then redo all the
> code duplication work for every frame) ?

You get two options by that.
1) permanently modifying one code object to be traceable is
pushing a copy of the original "behind" by means of some
co_back pointer. This keeps the patched one where the
original was, and makes a global debugging version.

2) Creating a copy for one frame, and putting the original
in to an co_back pointer. This gives debugging just
for this one frame.

> > Then I'd redirect the code from the CALL_TRACE opcode completely
> > to a user-defined function.
> What user-defined function? I don't understand that either...
> Except the sys_tracefunc, what other (user-defined) function do we have here?
> Is it a Python or a C function?

I would suggest a Python function, of course.

> > Getting rid of the extra code object would be done by this function
> > when tracing is off.
> How exactly? This seems to be obvious for you, but obviously, not for me ;-)

If the permanent tracing "1)" is used, just restore the code object's
contents from the original in co_back, and drop co_back.
In the "2)" version, just pull the co_back into the frame's code pointer
and loose the reference to the copy. Occours automatically on frame

> > It also vanishes automatically when the frame is released.
> The function or the extra code object?

The extra code object.

> I'm confused. I didn't understand your idea.

Forget it, it isn't more than another brain fart :-)

ciao - chris

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