improve platform independence (#296)

* add os.devnull for platform independence

fixes #288

* add test for soft_barcode

* open devnull as binary

* add version identifier to pickle

src/escpos/capabilities.py

@@ -8,12 +8,13 @@ import six
 import yaml
 
 from tempfile import gettempdir
+import platform
 
 logging.basicConfig()
 logger = logging.getLogger(__name__)
 
 pickle_dir = environ.get('ESCPOS_CAPABILITIES_PICKLE_DIR', gettempdir())
-pickle_path = path.join(pickle_dir, 'capabilities.pickle')
+pickle_path = path.join(pickle_dir, '{v}.capabilities.pickle'.format(v=platform.python_version()))
 capabilities_path = environ.get(
     'ESCPOS_CAPABILITIES_FILE',
     path.join(path.dirname(__file__), 'capabilities.json'))

src/escpos/escpos.py

@@ -24,6 +24,8 @@ from re import match as re_match
 import barcode
 from barcode.writer import ImageWriter
 
+import os
+
 from .constants import ESC, GS, NUL, QR_ECLEVEL_L, QR_ECLEVEL_M, QR_ECLEVEL_H, QR_ECLEVEL_Q
 from .constants import QR_MODEL_1, QR_MODEL_2, QR_MICRO, BARCODE_TYPES, BARCODE_HEIGHT, BARCODE_WIDTH
 from .constants import BARCODE_FONT_A, BARCODE_FONT_B, BARCODE_FORMATS
@@ -487,11 +489,12 @@ class Escpos(object):
         barcode_class = barcode.get_barcode_class(barcode_type)
         my_code = barcode_class(data, writer=image_writer)
 
-        my_code.write("/dev/null", {
-            'module_height': module_height,
-            'module_width': module_width,
-            'text_distance': text_distance
-        })
+        with open(os.devnull, "wb") as nullfile:
+            my_code.write(nullfile, {
+                'module_height': module_height,
+                'module_width': module_width,
+                'text_distance': text_distance
+            })
 
         # Retrieve the Pillow image and print it
         image = my_code.writer._image

test/test_function_softbarcode.py

@@ -0,0 +1,16 @@
+#!/usr/bin/python
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
+import escpos.printer as printer
+import pytest
+
+
+def test_soft_barcode():
+    """just execute soft_barcode
+    """
+    instance = printer.Dummy()
+    instance.soft_barcode("ean8", "1234")
+