[Python-Dev] PEP 289 - Generator Expressions - Let's Move Forward

[Jeremy Hylton]

On Fri, 2004-04-30 at 09:30, Barry Warsaw wrote:
> On Fri, 2004-04-30 at 09:07, Armin Rigo wrote:
> 
> > This looks (a) cool and (b) a complete hack that nobody should be allowed to
> > do without messing with sys._getframe().
> 
> It reminds me a little bit of the dynamic binding in Emacs lisp.  As
> incredibly useful as that is sometimes, it's a disgusting hack. :)

The funny thing is that it's the result of a static scoping discipline
rather than dynamic scoping.  What's funny about it has more to do with
side-effects that scoping rules.  If the x_square function was returned
out of its defining block, there would be no way to rebind x and it
would not be possible to define a variable x local to the caller that
would affect it.

Put another way, it's possible to reason statically about what binding x
will use when x_square() is called.  It's the same technique you would
use to write an accumulator generator (that is, a function that returns
accumulator functions).  See the appendix of Paul Graham's essay:
http://www.paulgraham.com/icad.html

Jeremy

PS I do owe everyone a PEP on the subject of re-binding.