PdoBase: Forbid getting item with zero index (fixes #581)

canopen/pdo/base.py

@@ -39,18 +39,22 @@ def __init__(self, node: Union[LocalNode, RemoteNode]):
     def __iter__(self):
         return iter(self.map)
 
-    def __getitem__(self, key):
-        if isinstance(key, int) and (0x1A00 <= key <= 0x1BFF or   # By TPDO ID (512)
-                                     0x1600 <= key <= 0x17FF or   # By RPDO ID (512)
-                                     0 < key <= 512):             # By PDO Index
-            return self.map[key]
-        else:
-            for pdo_map in self.map.values():
-                try:
-                    return pdo_map[key]
-                except KeyError:
-                    # ignore if one specific PDO does not have the key and try the next one
-                    continue
+    def __getitem__(self, key: Union[int, str]):
+        if isinstance(key, int):
+            if key == 0:
+                raise KeyError("PDO index zero requested for 1-based sequence")
+            if (
+                0 < key <= 512  # By PDO Index
+                or 0x1600 <= key <= 0x17FF  # By RPDO ID (512)
+                or 0x1A00 <= key <= 0x1BFF  # By TPDO ID (512)
+            ):
+                return self.map[key]
+        for pdo_map in self.map.values():
+            try:
+                return pdo_map[key]
+            except KeyError:
+                # ignore if one specific PDO does not have the key and try the next one
+                continue
         raise KeyError(f"PDO: {key} was not found in any map")
 
     def __len__(self):