diff --git a/GPy/kern/_src/periodic.py b/GPy/kern/_src/periodic.py
index 36fcb596..23818007 100644
--- a/GPy/kern/_src/periodic.py
+++ b/GPy/kern/_src/periodic.py
@@ -8,6 +8,7 @@ from ...util.linalg import mdot
 from ...util.decorators import silence_errors
 from ...core.parameterization.param import Param
 from ...core.parameterization.transformations import Logexp
+from functools import reduce
 
 class Periodic(Kern):
     def __init__(self, input_dim, variance, lengthscale, period, n_freq, lower, upper, active_dims, name):
diff --git a/GPy/kern/_src/prod.py b/GPy/kern/_src/prod.py
index 84bd1e1d..27a15aab 100644
--- a/GPy/kern/_src/prod.py
+++ b/GPy/kern/_src/prod.py
@@ -5,6 +5,7 @@ import numpy as np
 from .kern import CombinationKernel
 from ...util.caching import Cache_this
 import itertools
+from functools import reduce
 
 class Prod(CombinationKernel):
     """
diff --git a/GPy/util/pca.py b/GPy/util/pca.py
index f87b9807..7168a28f 100644
--- a/GPy/util/pca.py
+++ b/GPy/util/pca.py
@@ -13,6 +13,7 @@ except:
 from numpy.linalg.linalg import LinAlgError
 from operator import setitem
 import itertools
+from functools import reduce
 
 class PCA(object):
     """
@@ -47,7 +48,7 @@ class PCA(object):
             X_ = numpy.ma.masked_array(X, inan)
             self.mu = X_.mean(0).base
             self.sigma = X_.std(0).base
-        reduce(lambda y,x: setitem(x[0], x[1], x[2]), itertools.izip(X.T, inan.T, self.mu), None)
+        reduce(lambda y,x: setitem(x[0], x[1], x[2]), zip(X.T, inan.T, self.mu), None)
         X = X - self.mu
         X = X / numpy.where(self.sigma == 0, 1e-30, self.sigma)
         return X
@@ -138,4 +139,4 @@ class PCA(object):
             pylab.tight_layout()
         except:
             pass
-        return plots
\ No newline at end of file
+        return plots