[Tutor] cartesian product recursive loop

[Kent Johnson]

Gabriel Farrell wrote:
>> > Each call to rloop() has its own local variables and its own state.
>> > Returning from one call doesn't pop all the way up the stack, it
>> > resumes execution at the point of call with the local state restored
>> > to what it was before the call.
>>     
>
> Okay, this was the main abstraction I was missing, and you've spelled
> it out clearly.  It seems like such an "intelligent" way to handle the
> flow -- I think that's what threw me off.
>   
This is typical behavior for many languages, not special to Python. 
Generally each invocation of a function will have its own stack frame.

> I read
> http://www.ferg.org/papers/debugging_in_python.html , imported pdb,
> and inserted pdb.set_trace() after
>
>     def rloop(seqin, listout, comb):
>
> I'm seeing now, by stepping through the program, how it flows.  Pdb is
> pretty awesome!  I had a feeling there was something like different
> levels of loops going on, but I didn't get it before.  
>   
Impressive that you picked up pdb so easily. You might be interested in 
a debugger with a GUI, there are several for Python. A primitive one is 
part of IDLE. I like winpdb. Other dev tools have Python debugger 
support as well.
> Thanks, Kent!
You're welcome, it's very gratifying to see the light go on like this :-)

Kent