Dictionary that remembers insertion order
od.clear() -> None. Remove all items from od.
od.copy() -> a shallow copy of od
OD.fromkeys(S[, v]) -> New ordered dictionary with keys from S and values equal to v (which defaults to None).
od.popitem() -> (k, v)
Return and remove a (key, value) pair. Pairs are returned in LIFO order if last is true or FIFO order if false.