added Python six compatibility layer (#10)

added dependency to `six` for better Python 2/3 compatibility

pysstv/color.py

@@ -1,12 +1,6 @@
 #!/usr/bin/env python
-
 from __future__ import division
-try:  # python 2/3 compatibility
-    xrange  # will fail in python 3
-except NameError:
-    pass
-else:
-    range = xrange
+from six.moves import range
 from pysstv.sstv import byte_to_freq, FREQ_BLACK, FREQ_WHITE, FREQ_VIS_START
 from pysstv.grayscale import GrayscaleSSTV
 from itertools import chain
@@ -14,6 +8,7 @@ from itertools import chain
 
 RED, GREEN, BLUE = range(3)
 
+
 class ColorSSTV(GrayscaleSSTV):
     def on_init(self):
         self.pixels = self.image.load()

pysstv/grayscale.py

@@ -1,13 +1,7 @@
 #!/usr/bin/env python
 
 from __future__ import division
-
-try:  # python 2/3 compatibility
-    xrange  # will fail in python 3
-except NameError:
-    pass
-else:
-    range = xrange
+from six.moves import range
 from pysstv.sstv import SSTV, byte_to_freq
 
 

pysstv/sstv.py

@@ -1,24 +1,13 @@
 #!/usr/bin/env python
 
 from __future__ import division, with_statement
+from six.moves import range
+from six.moves import map
+from six.moves import zip
 from math import sin, pi
 from random import random
 from contextlib import closing
-try:
-    import itertools.imap as map  # python 2
-except ImportError:
-    pass  # python 3
-try:
-    import itertools.izip as zip  # python 2
-except ImportError:
-    pass  # python 3
 from itertools import cycle, chain
-try:  # python 2/3 compatibility
-    xrange  # will fail in python 3
-except NameError:
-    pass
-else:
-    range = xrange
 from array import array
 import wave
 

requirements.txt

@@ -1,3 +1,4 @@
+six==1.10.0
 Pillow==2.2.1
 mock==1.0.1
 nose==1.3.0