Yield multiple values

Because gen() returns a generator (a single item - so it can't be unpacked as two), it needs to be advanced first to get the values...

g = gen()
a, b = next(g)

It works with list because that implicitly consumes the generator.

Can we further make this a generator? Something like this:

g = gen();
def yield_g():
    yield g.next();
    k1,k2 = yield_g();

and therefore list(k1) would give [0,1,2,3,4] and list(k2) would give [1,2,3,4,5].

Keep your existing generator, and use izip (or zip):

from itertools import izip
k1, k2 = izip(*gen())

Your function gen returns a generator and not values as you might expect judging from the example you gave. If you iterate over the generator the pairs of values will be yielded:

In [2]: def gen():
   ...:     for i in range(5):
   ...:         yield i, i+1
   ...:         

In [3]: for k1, k2 in gen():
   ...:     print k1, k2
   ...:     
0 1
1 2
2 3
3 4
4 5