Generate Cartesian Products with Itertools Incrementally

[bowlofred]

The first two elements of the list you want aren't products at all, unless you extend the range of possibilities like a = ['', 'a', 'b'].

If you do that, then you could generate them and sort the result. But I'm not sure I understand exactly what list you want.

>>> a = ['', 'a', 'b']
>>> b = ['', '1', '2']
>>> sorted(["".join(x) for x in product(a,b)], key=len)
['', '1', '2', 'a', 'b', 'a1', 'a2', 'b1', 'b2']