Favorite non-python language trick?

[Rocco Moretti]

Joseph Garvin wrote:

> I'm curious -- what is everyone's favorite trick from a non-python 
> language? And -- why isn't it in Python?

I'm not aware of a language that allows it, but recently I've found 
myself wanting the ability to transparently replace objects. For 
example, if you have a transparent wrapper class around a certain 
object, and then determine that you no longer need to wrap the object, 
you can say the magic incantation, and the wrapper instance is replaced 
by what it is wrapping everywhere in the program. Or you have a complex 
math object, and you realize you can reduce it to a simple integer, you 
can substitue the integer for the math object, everywhere.

I mainly look for it in the "object replaces self" form, but I guess you 
could also have it for arbitrary objects, e.g. to wrap a logging object 
around a function, even if you don't have access to all references of 
that function.

Why isn't it in Python? It's completely counter to the conventional 
object semantics.