In python, using the range function actually creates a list which it stores in memory. However, using xrange just iterates through the numbers.

range(0,5000) takes up more memory than xrange(0,5000)

Here is a quick example of what I mean:

range.py:

import sys

for i in range(0,int(sys.argv[1])):
        pass

print " "

xrange.py:

import sys

for i in xrange(0,int(sys.argv[1])):
        pass

print " "

[$] time python range.py 10000000

real    0m1.139s
user    0m0.911s
sys     0m0.228s

[$] time python xrange.py 10000000

real    0m0.506s
user    0m0.502s
sys     0m0.004s