remove six usage (unnecessary starting python 2.6)

examples/parallel/pi/pidigits.py

@@ -20,7 +20,6 b' from __future__ import division, with_statement'
 
 import numpy as np
 from matplotlib import pyplot as plt
-from six import advance_iterator
 
 # Top-level functions
 
@@ -100,8 +99,8 b' def two_digit_freqs(digits, normalize=False):'
     Consume digits of pi and compute 2 digits freq. counts.
     """
     freqs = np.zeros(100, dtype='i4')
-    last = advance_iterator(digits)
-    this = advance_iterator(digits)
+    last = next(digits)
+    this = next(digits)
     for d in digits:
         index = int(last + this)
         freqs[index] += 1
@@ -120,7 +119,7 b' def n_digit_freqs(digits, n, normalize=False):'
     freqs = np.zeros(pow(10,n), dtype='i4')
     current = np.zeros(n, dtype=int)
     for i in range(n):
-        current[i] = advance_iterator(digits)
+        current[i] = next(digits)
     for d in digits:
         index = int(''.join(map(str, current)))
         freqs[index] += 1