Import fixes for Py3

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):

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):
     """