Ring arithmetic in Python. Condensed version

ring_condensed.py

from itertools import islice, cycle, tee

def a(n, dict_class=dict):
    a, b = tee(cycle(dict_class() for __ in range(n)))
    for d in islice(a, n):
        d.update(dict(enumerate(islice(b, n))))
        ret = next(b)
    return ret

class IdDict(dict):
    def __getitem__(self, __key):
        return dict.__getitem__(self, id(__key))

    def __setitem__(self, __key, __value):
        dict.__setitem__(self, id(__key), __value)

class g(IdDict):
    def __init__(self, base_dict, init_val, next_val_f):
        # Start with init_val, and call next_val_f for each item
        curr = {k: init_val for k in base_dict.keys()}
        for d in base_dict.values():
            self[d] = curr
            # add k to each v
            curr = {k: next_val_f(k, v) for k, v in curr.items()}

d = a(100)
m = g(d, d[0], lambda k, v: v[k])
p = g(d, d[1], lambda k, v: m[v][k])
# 2**3 * 3 + 6 = 30?
assert m[p[d[3]][2]][3][6] is d[30]