[Python-Dev] An issue recently brought up in patch #872326 (generator expression)

[Guido van Rossum]

> > IIRC, most people agreed on that iterables in the generator expression need
> > to be pre-computed (including myself). But there's a recent issue about
> > that.
> 
> If we're capturing the value of free variables, is there
> any need to pre-compute the iterators?

A free variable might be a function that itself references globals (or
at least nonlocals) that might change.

There is also the issue of exceptions: I'd expect exceptions in the
toplevel (first) iterable to be raised immediately, and not when the
first element of the iterator is requested.

--Guido van Rossum (home page: http://www.python.org/~guido/)