[Python-Dev] Interactive Debugging of Python

[Skip Montanaro]

    Guido> What kind of limitations do other systems that support modifying
    Guido> a "live" program being debugged impose?  Only allowing
    Guido> modification of the function at the top of the stack might
    Guido> eliminate some problems, although there are still ways to mess
    Guido> up.

Frame objects maintain pointers to the active code objects, locals and
globals, so modifying a function object's code or globals shouldn't have any
effect on currently executing frames, right?  I assume frame objects do the
usual INCREF/DECREF dance, so the old code object won't get deleted before
the frame object is tossed.

    Guido> But what would it do when we changed a global variable?  Say a
    Guido> module originally contains a statement "x = 0".  Now we change
    Guido> the source code to say "x = 100".  Should we change the variable
    Guido> x?  Suppose that x is modified by some of the computations in the
    Guido> module, and the that, after some computations, the actual value
    Guido> of x was 50.  Should the "recompile" reset x to 100 or leave it
    Guido> alone?

I think you should note the change for users and give them some way to
easily pick between old initial value, new initial value or current value.

    Guido> Please, no more posts about Scheme.  Each new post mentioning
    Guido> call/cc makes it *less* likely that something like that will ever
    Guido> be part of Python.  "What if Guido's brain exploded?" :-)

I agree.  I see call/cc or set! and my eyes just glaze over...

Skip Montanaro	| Mojam: "Uniting the World of Music" http://www.mojam.com/
skip at mojam.com  | Musi-Cal: http://www.musi-cal.com/
518-372-5583