gistfile1.txt

r1 = {'a': {'q': 1, 'w': 2}, 'b': {'q': 3, 'w': 4}} 
r2 = {'a': {'q': 5, 'w': 7}, 'b': {'q': 8, 'w': 2}} 
# ret = {'a': {'q': 6, 'w': 9}, 'b': {'q': 11, 'w': 6}}

def iter_dict(x, y):
    if not isinstance(x, dict):
        return map(lambda x: sum(x), zip(x, y))
    if isinstance(x.values()[0], dict):
        return dict(zip(x.keys(), map(lambda x:iter_dict(x[0], x[1]), zip(x.values(), y.values()))))
    return dict(zip(x.keys(), iter_dict(x.values(), y.values())))

print iter_dict(r1, r2)

Any Python version, haha. @liluo
Refer to https://gist.github.com/1958259.