diff --git a/atrcopy/cartridge.py b/atrcopy/cartridge.py
index b8bd323..78f0693 100644
--- a/atrcopy/cartridge.py
+++ b/atrcopy/cartridge.py
@@ -1,4 +1,6 @@
 from __future__ import absolute_import
+from builtins import str
+from builtins import object
 from collections import defaultdict
 
 import numpy as np
@@ -146,7 +148,7 @@ class A8CartHeader(object):
 
         if len(bytes) == 16:
             values = bytes.view(dtype=self.format)[0]
-            if values[0] != 'CART':
+            if values[0] != b'CART':
                 raise InvalidCartHeader
             self.cart_type = int(values[1])
             self.crc = int(values[2])
@@ -206,9 +208,9 @@ class AtariCartImage(DiskImageBase):
         return str(self.header)
 
     def read_header(self):
-        bytes = self.bytes[0:16]
+        data = self.bytes[0:16]
         try:
-            self.header = A8CartHeader(bytes)
+            self.header = A8CartHeader(data)
         except InvalidCartHeader:
             self.header = A8CartHeader()
             self.header.set_type(self.cart_type)
diff --git a/test/test_cart.py b/test/test_cart.py
index c5b1655..ba65fd6 100644
--- a/test/test_cart.py
+++ b/test/test_cart.py
@@ -1,4 +1,7 @@
 from __future__ import print_function
+from __future__ import division
+from builtins import object
+from past.utils import old_div
 from mock import *
 
 from atrcopy import AtariCartImage, SegmentData, InvalidDiskImage
@@ -10,7 +13,7 @@ class TestAtariCart(object):
 
     def get_cart(self, k_size, cart_type):
         data = np.zeros((k_size * 1024)+16, dtype=np.uint8)
-        data[0:4].view("|a4")[0] = 'CART'
+        data[0:4].view("|a4")[0] = b'CART'
         data[4:8].view(">u4")[0] = cart_type
         return data
 
@@ -47,7 +50,7 @@ class TestAtariCart(object):
             rawdata = SegmentData(data)
             image = AtariCartImage(rawdata, cart_type)
             image.parse_segments()
-            assert len(image.segments) == 1 + 1 + (k_size - main_size)/banked_size
+            assert len(image.segments) == 1 + 1 + old_div((k_size - main_size),banked_size)
             assert len(image.segments[0]) == 16
             assert len(image.segments[1]) == main_size * 1024
             assert len(image.segments[2]) == banked_size * 1024