fix issue #101

Author: gijzelaerr

snap7/util.py

@@ -128,24 +128,28 @@ def set_bool(_bytearray, byte_index, bool_index, value):
         _bytearray[byte_index] -= index_value
 
 
-def set_int(_bytearray, byte_index, _int):
+def set_int(bytearray_, byte_index, _int):
     """
     Set value in bytearray to int
     """
     # make sure were dealing with an int
     _int = int(_int)
     _bytes = struct.unpack('2B', struct.pack('>h', _int))
-    _bytearray[byte_index:byte_index + 2] = _bytes
+    bytearray_[byte_index:byte_index + 2] = _bytes
+    return bytearray_
 
 
-def get_int(_bytearray, byte_index):
+def get_int(bytearray_, byte_index):
     """
     Get int value from bytearray.
 
     int are represented in two bytes
     """
-    data = _bytearray[byte_index:byte_index + 2]
-    value = struct.unpack('>h', struct.pack('2B', *data))[0]
+    data = bytearray_[byte_index:byte_index + 2]
+    data[1] = data[1] & 0xff
+    data[0] = data[0] & 0xff
+    packed = struct.pack('2B', *data)
+    value = struct.unpack('>h', packed)[0]
     return value
 
 

test/test_util.py

@@ -1,7 +1,7 @@
 import unittest
 import re
 
-from snap7 import util
+from snap7 import util, snap7types
 
 
 test_spec = """
@@ -72,6 +72,14 @@ def test_set_int(self):
         row['ID'] = 259
         self.assertEqual(row['ID'], 259)
 
+    def test_set_int_roundtrip(self):
+        DB1 = (snap7types.wordlen_to_ctypes[snap7types.S7WLByte]*4)()
+
+        for i in range(-(2**15)+1, (2**15)-1):
+            util.set_int(DB1, 0, i)
+            result = util.get_int(DB1, 0)
+            self.assertEqual(i, result)
+
     def test_get_int_values(self):
         test_array = bytearray(_bytearray)
         row = util.DB_Row(test_array, test_spec, layout_offset=4)