On Thu, 31 Jan 2013 02:49:31 +1100, Chris Angelico wrote: > it's worth > noting that list appending is not going to be O(N*N), because it's going > to allow room for expansion.
This is true for list.append, which is amortized constant time. But it is not true for list addition, alist + blist, which is O(N**2) and hence gets really, really slow: steve@runes:~$ python -m timeit "L = []" "for i in xrange(1000): L = L + [1]" 100 loops, best of 3: 3.08 msec per loop steve@runes:~$ python -m timeit "L = []" "for i in xrange(5000): L = L + [1]" 10 loops, best of 3: 71 msec per loop steve@runes:~$ python -m timeit "L = []" "for i in xrange(25000): L = L + [1]" 10 loops, best of 3: 2.06 sec per loop Notice that as the number of list additions goes up by a factor of 5, the time taken goes up by a factor of 25. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
