Clarify ODVariable.data_type cannot be None (#666)

Use a simple integer zero as dummy value for "unset" in instances.
This fixes some type checker errors.  Add type hints for functions
involving those values.

Fix test coverage for unset and unknown data type.

Author: acolomb

canopen/objectdictionary/__init__.py

@@ -366,7 +366,7 @@ def __init__(self, name: str, index: int, subindex: int = 0):
         #: The value of this variable stored in the object dictionary
         self.value: Optional[int] = None
         #: Data type according to the standard as an :class:`int`
-        self.data_type: Optional[int] = None
+        self.data_type: int = 0
         #: Access type, should be "rw", "ro", "wo", or "const"
         self.access_type: str = "rw"
         #: The variable represents a DOMAIN ObjectType
@@ -480,7 +480,7 @@ def encode_raw(self, value: Union[int, float, str, bytes, bytearray]) -> bytes:
                 return self.STRUCT_TYPES[self.data_type].pack(value)
             except struct.error:
                 raise ValueError("Value does not fit in specified type")
-        elif self.data_type is None:
+        elif not self.data_type:
             raise ObjectDictionaryError("Data type has not been specified")
         else:
             raise TypeError(

canopen/objectdictionary/eds.py

@@ -4,7 +4,7 @@
 import logging
 import re
 from configparser import NoOptionError, NoSectionError, RawConfigParser
-from typing import TYPE_CHECKING
+from typing import Any, TYPE_CHECKING
 
 from canopen.objectdictionary import (
     ODArray,
@@ -204,7 +204,7 @@ def import_from_node(node_id: int, network: canopen.network.Network):
     return od
 
 
-def _calc_bit_length(data_type):
+def _calc_bit_length(data_type: int) -> int:
     if data_type == datatypes.INTEGER8:
         return 8
     elif data_type == datatypes.INTEGER16:
@@ -215,7 +215,7 @@ def _calc_bit_length(data_type):
         return 64
     else:
         raise ValueError(
-            f"Invalid data_type '{data_type}', expecting a signed integer data_type."
+            f"Invalid data_type 0x{data_type:04X}, expecting an integer data_type."
         )
 
 
@@ -229,7 +229,7 @@ def _signed_int_from_hex(hex_str, bit_length):
         return number
 
 
-def _convert_variable(node_id, var_type, value):
+def _convert_variable(node_id: int, var_type: int, value: Any) -> Any:
     if var_type in (datatypes.OCTET_STRING, datatypes.DOMAIN):
         return bytes.fromhex(value)
     elif var_type in (datatypes.VISIBLE_STRING, datatypes.UNICODE_STRING):
@@ -245,7 +245,7 @@ def _convert_variable(node_id, var_type, value):
             return int(value, 0)
 
 
-def _revert_variable(var_type, value):
+def _revert_variable(var_type: int, value: Any) -> Any:
     if value is None:
         return None
     if var_type in (datatypes.OCTET_STRING, datatypes.DOMAIN):

test/test_od.py

@@ -171,6 +171,15 @@ def test_domain(self):
         self.assertEqual(var.decode_raw(b"zero terminated\x00"), b"zero terminated\x00")
         self.assertEqual(var.encode_raw(b"testing"), b"testing")
 
+    def test_unknown_data_type(self):
+        var = od.ODVariable("Test unknown", 0x1000)
+        # data_type intentionally left at default (unset)
+        with self.assertRaises(od.ObjectDictionaryError):
+            var.encode_raw(42)
+        var.data_type = 0x7F  # from Device profile specific Standard Data types
+        with self.assertRaises(TypeError):
+            var.encode_raw(42)
+
 
 class TestAlternativeRepresentations(unittest.TestCase):