Apparently xrange is faster but I have no idea why it's faster (and no proof besides the anecdotal so far that it is faster) or what besides that is different about
for i in range(0, 20):
for i in xrange(0, 20):
In Python 2.x:
range creates a list, so if you do range(1, 10000000) it creates a list in memory with 9999999 elements.
xrange is a sequence object that evaluates lazily.
In Python 3:
range does the equivalent of Python 2's xrange. To get the list, you have to explicitly use list(range(...)).xrange no longer exists.