Add compatibility with python 3 - relative imports, fix xrange, fix tests

.travis.yml

@@ -1,5 +1,7 @@
 language: python
 python:
   - "2.7"
+  - "3.6"
+  - "3.7"
 # command to run tests
 script: python test.py

test.py

@@ -5,7 +5,12 @@ import sys
 import os
 import unittest
 import codecs
-from mock import patch, Mock, MagicMock
+
+if sys.version_info[0] < 3:
+    from mock import patch, Mock, MagicMock
+else:
+    from unittest.mock import patch, Mock, MagicMock
+    
 mock_socket = MagicMock(name='zk.socket')
 sys.modules['zk.socket'] = mock_socket
 from zk import ZK, const

zk/base.py

@@ -5,11 +5,11 @@ from socket import AF_INET, SOCK_DGRAM, SOCK_STREAM, socket, timeout
 from struct import pack, unpack
 import codecs
 
-from zk import const
-from zk.attendance import Attendance
-from zk.exception import ZKErrorConnection, ZKErrorResponse, ZKNetworkError
-from zk.user import User
-from zk.finger import Finger
+from . import const
+from .attendance import Attendance
+from .exception import ZKErrorConnection, ZKErrorResponse, ZKNetworkError
+from .user import User
+from .finger import Finger
 
 
 def safe_cast(val, to_type, default=None):
@@ -302,7 +302,7 @@ class ZK(object):
 
     def __reverse_hex(self, hex):
         data = ''
-        for i in reversed(xrange(len(hex) / 2)):
+        for i in reversed(range(len(hex) / 2)):
             data += hex[i * 2:(i * 2) + 2]
         return data