add support for python 3

pspec_new.py

@@ -1,7 +1,9 @@
 """Compute power spectra"""
 
 from __future__ import division
+from __future__ import print_function
 
+from builtins import range
 import argparse
 import sys
 import textwrap
@@ -840,7 +842,7 @@ def main(arg):
             "cos_vB",
             "vz",
         ]:
-            for i in xrange(ns):
+            for i in range(ns):
                 pspec, kbins, pspec2, fbins = pspectrum(
                     pcubes2[v][:, :, i], cubes_k["k"][:, :, i], kbins, knorm, arg.fbins
                 )