Richard Jones' Log: Python's Deficient Generators

I've had people try to explain why Python's generators are deficient before and the light just went off. To flatten an arbitrarily deep (though stack-limited) nested iterator structure, I wrote:

>>> def flatten(iterable):
...  for elem in iterable:
...   if hasattr(elem, '__iter__'):
...    for sub in flatten(elem): yield sub
...   else:
...    yield elem
... 
>>> list(flatten([[1,2,3],[[2,3],4],[4,5,6]]))
[1, 2, 3, 2, 3, 4, 4, 5, 6]

The key failing is that inner "for" loop. It's called "trampolining" as described by David Beazley. If I could somehow yield to the top of the generator stack it'd be unnecessary. It'd look something like PEP 380:

>>> def flatten(iterable):
...  for elem in iterable:
...   if hasattr(elem, '__iter__'):
...    yield from flatten(elem)
...   else:
...    yield elem
... 
>>> list(flatten([[1,2,3],[[2,3],4],[4,5,6]]))
[1, 2, 3, 2, 3, 4, 4, 5, 6]

Too bad there's a moratorium on changes :)

Updated to include the PEP, thanks ulrik!