To ensure the lookup algorithm terminates, there must be at least one Unused
slot (NULL key) in the table.
The value ma_fill is the number of non-NULL keys (sum of Active and Dummy);
ma_used is the number of non-NULL, non-dummy keys (== the number of non-NULL
values == the number of Active items).
To avoid slowing down lookups on a near-full table, we resize the table when
it's two-thirds full.
To ensure the lookup algorithm terminates, there must be at least one Unused slot (NULL key) in the table. The value ma_fill is the number of non-NULL keys (sum of Active and Dummy); ma_used is the number of non-NULL, non-dummy keys (== the number of non-NULL values == the number of Active items). To avoid slowing down lookups on a near-full table, we resize the table when it's two-thirds full.
*/ /// subclass of PyObjec