py-billow

Module have several types: ring (double linked list), pair(light weight tuple), Nil-singletone.

In billow SQL(NULL) for now is 'billow.Nil' type with some aggregate functions on cpython release, and 'expectone' as bridge aggregated function together with 'coalesce', 'count', 'min', 'max', 'minmax'. All group function gets as tuple arguments - {name}'_at', and iteratable function - {name}'_it' for fun python constructor - for free on memory limits, because it is the same C function.