How to program test(expr) ?

Thu Aug 30 03:33:58 EDT 2012

Am 29.08.2012 17:04, schrieb Franck Ditter:
> I use Python 3.2.3 + Idle.
> Is it possible to program test(e) which takes
> an expression e and whose execution produces
> at the toplevel an echo of e and the effects
> and result of its evaluation ?

Yes, the key to this is using a lambda expression.
> # file foo.py
> def foo(x) :
> print('x =',x)
> return x+1
>> test(foo(5))

def test(exp):
 global print
 print_saved = print
 print = my_print
 res = exp()
 print = print_saved
 return res
test(lambda: foo(5))
The idea is to run the callable expression inside a modified 
environment, in the sketch above it intercepts the calles to print() 
using a separate my_print() function. Note that the calling syntax is 
slightly different than the one you would have wanted, don't know if 
that is important.
Things I'll leave to you:
 - exception handling
 - exception forwarding
 - intercepting other environment accesses
 - putting all that into a context manager :)
Good luck!
Uli