[Python-Dev] PEP 553

Terry Reedy tjreedy at udel.edu
Mon Oct 2 16:10:06 EDT 2017

On 10/2/2017 10:45 AM, Guido van Rossum wrote:
> On Sun, Oct 1, 2017 at 11:15 PM, Terry Reedy <tjreedy at udel.edu 
> <mailto:tjreedy at udel.edu>> wrote:
>     On 10/2/2017 12:44 AM, Guido van Rossum wrote:
>         - There's no rationale for the *args, **kwds part of the
>         breakpoint() signature. (I vaguely recall someone on the mailing
>         list asking for it but it seemed far-fetched at best.)
>     If IDLE's event-driven GUI debugger were rewritten to run in the
>     user process, people wanting to debug a tkinter program should be
>     able to pass in their root, with its mainloop, rather than having
>     the debugger create its own, as it normally would.  Something else
>     could come up.
> But if they care so much, they could also use a small wrapper as the 
> sys.breakpointhook that retrieves the root and calls the IDLE debugger 
> with that.

'They' include beginners that need the simplicity of breakpoint() the most.

> Why is adding the root to the breakpoint() call better than 
> that? To me, the main attraction for breakpoint is that there's 
> something I can type quickly and insert at any point in the code.

I agree.

> During a debugging session
> I may try setting it in many different places. If I 
> have to also pass the root each time I type "breakpoint()" that's just 
> an unnecessary detail compared to having it done automatically by the hook.

Even though pdb.set_trace re-initializes each call, idb.whatever should 
*not*. So it should set something that can be queried. My idea was that 
a person should pass root only on the first call.  But that founders on 
the fact that 'first call' may not be deterministic.

if cond:
<more stuff>

Besides which, someone might insert breakpoint() before creating a root.

So I will try instead initializing with
iroot = tk._default_root if tk._default_root else tk.Tk()
and stick with iroot.update() and avoid i.mainloop()

A revised tk-based debugger, closer to pdb than it is now, will require 
some experimentation.  I would like to be able to use it to debug IDLE 
run from a command line, and that will be a fairly severe test of 
compatibility with a tkinter application.

You could approve breakpoint() without args now and add them if and when 
there were more convincing need.

Terry Jan Reedy

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