Hooking exceptions outside of call stack

[Josiah Carlson]

Warren Stringer wrote:
> Here is what I would like to do:
> 
> #------------------------------------------------------------
> a = Tr3()              # implements domain specific language
> a.b = 1                # this works, Tr3 overrides __getattr__
> a.__dict__['b'] = 2    # just so you know that b is local
> a[b] = 3               # I want to resolve locally, but get:
> 
> Traceback (most recent call last): ...
>     exec cmd in globals, locals ...
> NameError: global name 'b' is not defined
> #------------------------------------------------------------

Note that your a[b]=3 is the same as '__ = b;a[__]=3'  You get that 
exception because b is not a bound name in the namespace you are 
currently using.  In order to get what you want, you will either need to 
use a['b'] = 3, a.b = 3, or a method that I refuse to describe to you.

> This is intended for production code.

The reason I refuse to describe to you the method that could 'solve' 
your particular problem is because it would be very difficult to 
differentiate between what you *want* to happen, and actual errors, 
which would make production code *very* difficult to get right.

As an alternative to a['b'], you could use a[Z.b], for an object Z:

     class Z:
         def __getattr__(self, a):
             return a

     Z = Z()

Which will have much less potential for destroying the maintainability 
and testability of your production code than hooking any trace function.


  - Josiah