What is a mechanism equivalent to "trace variable w ..." in Tcl for Python?

[Ned Batchelder]

On Friday, September 30, 2016 at 2:16:10 PM UTC-4, Les Cargill wrote:
> A really interesting design approach in Tcl is to install a callback
> when a variable is written to. This affords highly event-driven 
> programming.
> 
> Example ( sorry; it's Tcl  ) :
> 
> 

(I can't read Tcl, sorry)

> 
> What is an equivalent mechanism in Python?

There's no way* to hook into "x = 2", but you could hook into "x.a = 2"
if you wanted do, by defining __setattr__ on x's class.

*OK, there might be some crazy hack involving your own class as the
globals for a module or something, but it sounds ill-advised.

--Ned.