[Python-Dev] Why do we need Traceback Objects?

[Christian Tismer]

Vladimir Marangozov wrote:
> 
> [Christian]
> > > When I look into tracebacks, it turns out to be just a chain
> > > like the frame chain, but upward down. It holds references
> > > to the frames in a 1-to-1 manner, and it keeps copies of
> > > f->f_lasti and f->f_lineno. I don't see why this is needed.
> > > ...
> > > Does this make sense? Do I miss something?
> >
> 
> [Guido]
> > Yes.  It is quite possible to have multiple stack traces lingering
> > around that all point to the same stack frames.
> 
> This reminds me that some time ago I made an experimental patch for
> removing SET_LINENO. There was the problem of generating callbacks
> for pdb (which I think I solved somehow but I don't remember the
> details). I do remember that I had to look at pdb again for some
> reason. Is there any interest in reviving this idea?

This is a very cheap opcode (at least in my version).
What does it buy? Can you drop the f_lineno field
from frames, and calculate it for the frame's f_lineno
attribute?

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