diff --git a/KDEpy/BaseKDE.py b/KDEpy/BaseKDE.py
index 48f2743..5ddeca2 100644
--- a/KDEpy/BaseKDE.py
+++ b/KDEpy/BaseKDE.py
@@ -3,16 +3,24 @@
 """
 Module for the BaseKDE class.
 """
+from __future__ import absolute_import, division, print_function
+
+import six
 import numbers
 import numpy as np
-from abc import ABC, abstractmethod
-from collections.abc import Sequence
+from abc import ABCMeta, abstractmethod
 from KDEpy.kernel_funcs import _kernel_functions
 from KDEpy.bw_selection import _bw_methods
 from KDEpy.utils import autogrid
 
+if six.PY3:
+    from collections.abc import Sequence
+else:
+    from collections import Sequence
+
 
-class BaseKDE(ABC):
+@six.add_metaclass(ABCMeta)
+class BaseKDE:
     """
     Abstract Base Class for every Kernel Density Estimator.
 
@@ -31,7 +39,7 @@ class BaseKDE(ABC):
     _bw_methods = _bw_methods
 
     @abstractmethod
-    def __init__(self, kernel: str, bw: float):
+    def __init__(self, kernel, bw):
         """Initialize the kernel density estimator.
 
         The return type must be duplicated in the docstring to comply
diff --git a/KDEpy/FFTKDE.py b/KDEpy/FFTKDE.py
index d2d0dfa..3ecb4d2 100644
--- a/KDEpy/FFTKDE.py
+++ b/KDEpy/FFTKDE.py
@@ -3,6 +3,8 @@
 """
 Module for the FFTKDE.
 """
+from __future__ import division, absolute_import, print_function
+
 import numbers
 import warnings
 import numpy as np
@@ -69,7 +71,7 @@ class FFTKDE(BaseKDE):
 
     def __init__(self, kernel="gaussian", bw=1, norm=2):
         self.norm = norm
-        super().__init__(kernel, bw)
+        super(FFTKDE, self).__init__(kernel, bw)
         assert isinstance(self.norm, numbers.Number) and self.norm > 0
 
     def fit(self, data, weights=None):
@@ -99,7 +101,7 @@ def fit(self, data, weights=None):
         """
 
         # Sets self.data
-        super().fit(data, weights)
+        super(FFTKDE, self).fit(data, weights)
         return self
 
     def evaluate(self, grid_points=None):
@@ -131,7 +133,7 @@ def evaluate(self, grid_points=None):
         """
 
         # This method sets self.grid_points and verifies it
-        super().evaluate(grid_points)
+        super(FFTKDE, self).evaluate(grid_points)
 
         # Extra verification for FFTKDE (checking the sorting property)
         if not grid_is_sorted(self.grid_points):
@@ -186,7 +188,9 @@ def evaluate(self, grid_points=None):
         assert (dx * L <= real_bw).all()
 
         # Evaluate the kernel once
-        grids = [np.linspace(-dx * L, dx * L, int(L * 2 + 1)) for (dx, L) in zip(dx, L)]
+        grids = [
+            np.linspace(-dx * Li, dx * Li, int(Li * 2 + 1)) for (dx, Li) in zip(dx, L)
+        ]
         kernel_grid = cartesian(grids)
         kernel_weights = self.kernel(kernel_grid, bw=self.bw, norm=self.norm)
 
diff --git a/KDEpy/NaiveKDE.py b/KDEpy/NaiveKDE.py
index 0cad600..2c15128 100644
--- a/KDEpy/NaiveKDE.py
+++ b/KDEpy/NaiveKDE.py
@@ -3,6 +3,8 @@
 """
 Module for the NaiveKDE.
 """
+from __future__ import division, absolute_import, print_function
+
 import numbers
 import itertools
 import numpy as np
@@ -50,7 +52,7 @@ class NaiveKDE(BaseKDE):
     """
 
     def __init__(self, kernel="gaussian", bw=1, norm=2):
-        super().__init__(kernel, bw)
+        super(NaiveKDE, self).__init__(kernel, bw)
         self.norm = norm
 
     def fit(self, data, weights=None):
@@ -80,7 +82,7 @@ def fit(self, data, weights=None):
         >>> x, y = kde()
         """
         # Sets self.data
-        super().fit(data, weights)
+        super(NaiveKDE, self).fit(data, weights)
         return self
 
     def evaluate(self, grid_points=None):
@@ -113,7 +115,7 @@ def evaluate(self, grid_points=None):
         # This method sets self.grid points and verifies it
         # NaiveKDE does not convert the bw to a scalar, since a vector is
         # allowed too.
-        super().evaluate(grid_points, bw_to_scalar=False)
+        super(NaiveKDE, self).evaluate(grid_points, bw_to_scalar=False)
 
         # Create zeros on the grid points
         evaluated = np.zeros(self.grid_points.shape[0])
diff --git a/KDEpy/TreeKDE.py b/KDEpy/TreeKDE.py
index 2aa3fc6..f14b77c 100644
--- a/KDEpy/TreeKDE.py
+++ b/KDEpy/TreeKDE.py
@@ -3,6 +3,8 @@
 """
 Module for the TreeKDE.
 """
+from __future__ import division, absolute_import, print_function
+
 from scipy.spatial import cKDTree
 import numbers
 import numpy as np
@@ -60,7 +62,7 @@ class TreeKDE(BaseKDE):
     """
 
     def __init__(self, kernel="gaussian", bw=1, norm=2.0):
-        super().__init__(kernel, bw)
+        super(TreeKDE, self).__init__(kernel, bw)
         self.norm = norm
 
     def fit(self, data, weights=None):
@@ -90,7 +92,7 @@ def fit(self, data, weights=None):
         >>> x, y = kde()
         """
         # Sets self.data
-        super().fit(data, weights)
+        super(TreeKDE, self).fit(data, weights)
         return self
 
     def evaluate(self, grid_points=None, eps=10e-4):
@@ -126,7 +128,7 @@ def evaluate(self, grid_points=None, eps=10e-4):
         """
 
         # This method sets self.grid points and verifies it
-        super().evaluate(grid_points)
+        super(TreeKDE, self).evaluate(grid_points)
 
         evaluated = np.zeros(self.grid_points.shape[0])
 
diff --git a/KDEpy/__init__.py b/KDEpy/__init__.py
index 717127a..bfaf5f6 100644
--- a/KDEpy/__init__.py
+++ b/KDEpy/__init__.py
@@ -2,6 +2,8 @@
 # -*- coding: utf-8 -*-
 
 
+from __future__ import absolute_import, division, print_function
+
 from KDEpy.NaiveKDE import NaiveKDE
 from KDEpy.TreeKDE import TreeKDE
 from KDEpy.FFTKDE import FFTKDE
diff --git a/KDEpy/binning.py b/KDEpy/binning.py
index 8c37fcc..eb36316 100644
--- a/KDEpy/binning.py
+++ b/KDEpy/binning.py
@@ -29,6 +29,8 @@
   Journal of Computational and Graphical Statistics 3, no. 1 (March 1, 1994).
   https://doi.org/10.1080/10618600.1994.10474629.
 """
+from __future__ import division, absolute_import, print_function
+
 import numpy as np
 import itertools
 import functools
diff --git a/KDEpy/bw_selection.py b/KDEpy/bw_selection.py
index 681c00b..d6a70e8 100644
--- a/KDEpy/bw_selection.py
+++ b/KDEpy/bw_selection.py
@@ -3,6 +3,8 @@
 """
 Functions for bandwidth selection.
 """
+from __future__ import absolute_import, division, print_function
+
 import numpy as np
 import scipy
 import warnings
diff --git a/KDEpy/kernel_funcs.py b/KDEpy/kernel_funcs.py
index 06fea4b..8583c85 100644
--- a/KDEpy/kernel_funcs.py
+++ b/KDEpy/kernel_funcs.py
@@ -5,14 +5,21 @@
 is everywhere non-negative and whose integral evalutes to unity. Every kernel
 function takes an `x` of shape (obs, dims) and returns a y of shape (obs, 1).
 """
+from __future__ import division, absolute_import, print_function
 
 import numpy as np
-import collections.abc
 import numbers
 import functools
 from scipy.special import gamma, factorial2
 from scipy.stats import norm
 from scipy.optimize import brentq
+import six
+
+if six.PY3:
+    import collections.abc as collections_abc
+else:
+    import collections as collections_abc
+
 
 # In R, the following are implemented:
 # "gaussian", "rectangular", "triangular", "epanechnikov",
@@ -223,7 +230,7 @@ def sigmoid(x, dims=1):
     return 1 / (np.pi * np.cosh(x))
 
 
-class Kernel(collections.abc.Callable):
+class Kernel(collections_abc.Callable):
     def __init__(self, function, var=1, support=3):
         """
         Initialize a new kernel function.
diff --git a/KDEpy/tests/test_BaseKDE.py b/KDEpy/tests/test_BaseKDE.py
index e77f375..4ab1a9c 100644
--- a/KDEpy/tests/test_BaseKDE.py
+++ b/KDEpy/tests/test_BaseKDE.py
@@ -4,6 +4,8 @@
 API tests. Since BaseKDE is an abstract class, the testing is done using the
 naiveKDE class instead. The tests here are related to input types.
 """
+from __future__ import absolute_import, division, print_function
+
 import numpy as np
 from KDEpy.NaiveKDE import NaiveKDE
 import itertools
diff --git a/KDEpy/tests/test_FFTKDE.py b/KDEpy/tests/test_FFTKDE.py
index 41ab8b4..e50bf12 100644
--- a/KDEpy/tests/test_FFTKDE.py
+++ b/KDEpy/tests/test_FFTKDE.py
@@ -3,6 +3,8 @@
 """
 Tests for the FFTKDE.
 """
+from __future__ import absolute_import, division, print_function
+
 import numpy as np
 from KDEpy.FFTKDE import FFTKDE
 from KDEpy.NaiveKDE import NaiveKDE
diff --git a/KDEpy/tests/test_NaiveKDE.py b/KDEpy/tests/test_NaiveKDE.py
index b71c3d2..6a97bc8 100644
--- a/KDEpy/tests/test_NaiveKDE.py
+++ b/KDEpy/tests/test_NaiveKDE.py
@@ -4,6 +4,8 @@
 Tests for the NaiveKDE. The NaiveKDE is tested against various properties, and
 in turn more advanced implementations are tested against the NaiveKDE.
 """
+from __future__ import absolute_import, division, print_function
+
 import numpy as np
 from KDEpy.NaiveKDE import NaiveKDE
 import itertools
diff --git a/KDEpy/tests/test_TreeKDE.py b/KDEpy/tests/test_TreeKDE.py
index dc2a92c..7f9c986 100644
--- a/KDEpy/tests/test_TreeKDE.py
+++ b/KDEpy/tests/test_TreeKDE.py
@@ -3,6 +3,8 @@
 """
 Tests for the TreeKDE.
 """
+from __future__ import absolute_import, division, print_function
+
 import numpy as np
 from KDEpy.TreeKDE import TreeKDE
 import itertools
diff --git a/KDEpy/tests/test_api.py b/KDEpy/tests/test_api.py
index 05e3a69..5c40b32 100644
--- a/KDEpy/tests/test_api.py
+++ b/KDEpy/tests/test_api.py
@@ -5,6 +5,8 @@
 be equal for every implementation. Therefore it's important to have unit tests
 for the API.
 """
+from __future__ import absolute_import, division, print_function
+
 import numpy as np
 from KDEpy.FFTKDE import FFTKDE
 from KDEpy.NaiveKDE import NaiveKDE
diff --git a/KDEpy/tests/test_binning.py b/KDEpy/tests/test_binning.py
index 6c4c845..530dede 100644
--- a/KDEpy/tests/test_binning.py
+++ b/KDEpy/tests/test_binning.py
@@ -3,6 +3,8 @@
 """
 Tests for binning functions.
 """
+from __future__ import division, absolute_import, print_function
+
 import pytest
 import numpy as np
 from KDEpy.utils import autogrid
diff --git a/KDEpy/tests/test_estimator_vs_estimator.py b/KDEpy/tests/test_estimator_vs_estimator.py
index ecf878f..b56fe98 100644
--- a/KDEpy/tests/test_estimator_vs_estimator.py
+++ b/KDEpy/tests/test_estimator_vs_estimator.py
@@ -3,6 +3,8 @@
 """
 Test the implemented estimators against each other on simple data sets.
 """
+from __future__ import absolute_import, division, print_function
+
 import numpy as np
 from KDEpy.NaiveKDE import NaiveKDE
 from KDEpy.TreeKDE import TreeKDE
diff --git a/KDEpy/tests/test_kernel_funcs.py b/KDEpy/tests/test_kernel_funcs.py
index 1ba8dc8..3ba2ada 100644
--- a/KDEpy/tests/test_kernel_funcs.py
+++ b/KDEpy/tests/test_kernel_funcs.py
@@ -4,6 +4,8 @@
 Test the kernel functions K. Every kernel function is a radial basis function,
 i.e. it's a composition of a norm and a function defined on positive reals.
 """
+from __future__ import absolute_import, division, print_function
+
 import numpy as np
 import scipy
 from scipy.integrate import quad
diff --git a/KDEpy/tests/test_sorted_grid.py b/KDEpy/tests/test_sorted_grid.py
index 65e405f..4b61d17 100644
--- a/KDEpy/tests/test_sorted_grid.py
+++ b/KDEpy/tests/test_sorted_grid.py
@@ -3,6 +3,8 @@
 """
 Tests for verifying that grids obeys the sorting properties required for linear binning.
 """
+from __future__ import absolute_import, division, print_function
+
 import pytest
 import numpy as np
 from KDEpy.binning import grid_is_sorted  # Imported from .pyx to binning.py, then here
diff --git a/KDEpy/utils.py b/KDEpy/utils.py
index c27e782..dfea68b 100644
--- a/KDEpy/utils.py
+++ b/KDEpy/utils.py
@@ -3,6 +3,8 @@
 """
 Module for utility functions.
 """
+from __future__ import absolute_import, division, print_function
+
 import numpy as np
 import numbers
 
diff --git a/setup.py b/setup.py
index 2198d8b..14864dc 100644
--- a/setup.py
+++ b/setup.py
@@ -10,6 +10,7 @@
 from setuptools import Extension, setup
 import os
 import re
+from io import open
 
 HERE = os.path.abspath(os.path.dirname(__file__))