This is because it tries to increase the hash table size to the next
larger size when it is about 2/3rd full. Since the largest prime in
the table is
around 30000, somewhere around 20000 it will look for the next larger
prime, which isn't there...
--Guido van Rossum, CWI, Amsterdam <Guido.van.Rossum@cwi.nl>
URL: <http://www.cwi.nl/cwi/people/Guido.van.Rossum.html>