#!/usr/local/bin/python2 from itertools import chain chain_from_iterable = chain.from_iterable l = [[1,2,3,4,5], [6,7,8,9,0], [1,2,3,4,5], [6,7,8,9,0], [1,2,4,5]] for k in xrange(200000): list(chain_from_iterable([i for i in l]))