Hooking exceptions outside of call stack

[Warren Stringer]

Am still trying to hook a NameError exception and continue to run. After a
few more hours of searching the web and pouring over Martelli's book, the
closest I've come is:

>>> import sys
>>> def new_exit(arg=0):
...     print 'new_exit called'
...     #old_exit(arg)
...
>>> def hook(type, value, tb):
...     print 'hook called with', type
...     return
...
>>> sys.excepthook = hook
>>> old_exit = sys.exit
>>> sys.exit = new_exit
>>> a[b]=1 # would like to get new_exit called
hook called with exceptions.NameError
>>>
>>> def test():
...     sys.exit()
...
>>> test()
new_exit called

The interactive session is different from running in the IDE (am using
ActiveState's Visual Python) which exits just after the `a[b]=1` without
calling hook.  

Am I missing something? Perhaps this is the wrong approach? I want Python to
check a specific set of locals first, before checking globals. For instance:


    a.b[c]              

will call: 

    a.__getattr__('b')  

but an exception is thrown before: 

    a.b.__getitem__(c) 

Is there a way of intervening as `exec cmd in globals, locals` attempts to
translate 'c' into an object? I thought that trapping a NameError might
work. But now, I'm not so sure.

Many thanks,

\~/

> 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
> #------------------------------------------------------------
> 
> So far, I've tried capturing exceptions in __getattr__, __setitem__, and
> __setattr__, with no luck. I do NOT want to put `a[b]=3` inside a
> try...except block because I want to enable a command line `>>>a[b]=3`
> 
> Is there a way to hook a NameError exception outside of the call stack?
> Perhaps, inside Tr3.__init__ ? Is there a way of putting back unhandled
> NameError exceptions, so that they unwind the stack normally?
> 
> This is intended for production code.