Replace mapping in class PDO with proper PdoMaps object.

The mechanisms to lookup objects, implemented in class PdoMaps, did
not apply to the PDO class itself, because it simply used a dictionary
instead of a PdoMaps object.  That also violates the static typing
rules.

Make the PdoBase.maps attribute mandatory and accept only type
PdoMaps.  To allow a basically "empty" PdoMaps object, adjust its
constructor to skip adding entries when neither offset parameter is
given as non-zero.  Instead, access the PdoMaps.maps attribute
directly to inject the offset-based TX and RX PdoMap objects in the
PDO class constructor.  Add some explanation why relative indices
cannot be used here.

Author: acolomb

canopen/pdo/__init__.py

@@ -24,17 +24,19 @@ class PDO(PdoBase):
     :param tpdo: TPDO object holding the Transmit PDO mappings
     """
 
-    def __init__(self, node, rpdo, tpdo):
+    def __init__(self, node, rpdo: PdoBase, tpdo: PdoBase):
         super(PDO, self).__init__(node)
         self.rx = rpdo.map
         self.tx = tpdo.map
 
-        self.map = {}
-        # the object 0x1A00 equals to key '1' so we remove 1 from the key
+        self.map = PdoMaps(0, 0, self)
+        # Combine RX and TX entries, but only via mapping parameter index.  Relative index
+        # numbers would be ambiguous.
+        # The object 0x1A00 equals to key '1' so we remove 1 from the key
         for key, value in self.rx.items():
-            self.map[0x1600 + (key - 1)] = value
+            self.map.maps[self.rx.map_offset + (key - 1)] = value
         for key, value in self.tx.items():
-            self.map[0x1A00 + (key - 1)] = value
+            self.map.maps[self.tx.map_offset + (key - 1)] = value
 
 
 class RPDO(PdoBase):

canopen/pdo/base.py

@@ -34,7 +34,7 @@ class PdoBase(Mapping):
 
     def __init__(self, node: Union[LocalNode, RemoteNode]):
         self.network: canopen.network.Network = canopen.network._UNINITIALIZED_NETWORK
-        self.map: Optional[PdoMaps] = None
+        self.map: PdoMaps  # must initialize in derived classes
         self.node: Union[LocalNode, RemoteNode] = node
 
     def __iter__(self):
@@ -158,6 +158,9 @@ def __init__(self, com_offset: int, map_offset: int, pdo_node: PdoBase, cob_base
         self.maps: dict[int, PdoMap] = {}
         self.com_offset = com_offset
         self.map_offset = map_offset
+        if not com_offset and not map_offset:
+            # Skip generating entries without parameter index offsets
+            return
         for map_no in range(512):
             if com_offset + map_no in pdo_node.node.object_dictionary:
                 new_map = PdoMap(