modifier_callback should change one message per send

Alexander Bessman · Alexander Bessman · commit 1ea949dc7612 · 2019-09-30T21:25:56.000+02:00
diff --git a/can/broadcastmanager.py b/can/broadcastmanager.py
@@ -132,9 +132,9 @@ class ModifiableCyclicTaskABC(CyclicSendTaskABC):
 
     def _check_modifier_callback(self, modifier_callback):
         if modifier_callback is not None:
-            modified_msgs = modifier_callback(self.messages)
+            modified_msg = modifier_callback(self.messages[0])
 
-            if modified_msgs[0].arbitration_id != self.arbitration_id:
+            if modified_msg.arbitration_id != self.arbitration_id:
                 raise ValueError(
                     "The modifier callback function must not modify the "
                     "messages' arbitration ID."
@@ -219,9 +219,7 @@ def __init__(
         messages: Union[Sequence[Message], Message],
         period: float,
         duration: Optional[float] = None,
-        modifier_callback: Optional[
-            Callable[[Tuple[Message, ...]], Tuple[Message, ...]]
-        ] = None,
+        modifier_callback: Optional[Callable[[Message], Message]] = None,
     ):
         super().__init__(messages, period, duration)
         self.bus = bus
@@ -264,7 +262,8 @@ def _run(self):
                 started = time.perf_counter()
                 try:
                     if self.modifier_callback is not None:
-                        self.messages = self.modifier_callback(self.messages)
+                        modified_msg = self.modifier_callback(self.messages[msg_index])
+                        self.messages[msg_index].data = modified_msg.data
                     self.bus.send(self.messages[msg_index])
                 except Exception as exc:
                     log.exception(exc)
diff --git a/can/bus.py b/can/bus.py
@@ -176,9 +176,7 @@ def send_periodic(
         period: float,
         duration: Optional[float] = None,
         store_task: bool = True,
-        modifier_callback: Optional[
-            Callable[[Tuple[Message, ...]], Tuple[Message, ...]]
-        ] = None,
+        modifier_callback: Optional[Callable[[Message], Message]] = None,
     ) -> can.broadcastmanager.CyclicSendTaskABC:
         """Start sending messages at a given period on this bus.
 
@@ -200,6 +198,9 @@ def send_periodic(
         :param store_task:
             If True (the default) the task will be attached to this Bus instance.
             Disable to instead manage tasks manually.
+        :param modifier_callback:
+            Function which should be used to modify each message's data before
+            sending. Should take a Message as input and return the same.
         :return:
             A started task instance. Note the task can be stopped (and depending on
             the backend modified) by calling the :meth:`stop` method.
diff --git a/examples/cyclic_checksum.py b/examples/cyclic_checksum.py
@@ -32,13 +32,12 @@ def cyclic_checksum_send(bus):
     print("stopped cyclic send")
 
 
-def update_message(messages):
-    for m in messages:
-        counter = increment_counter(m)
-        checksum = compute_xbr_checksum(m, counter)
-        m.data[7] = (checksum << 4) + counter
+def update_message(message):
+    counter = increment_counter(message)
+    checksum = compute_xbr_checksum(message, counter)
+    message.data[7] = (checksum << 4) + counter
 
-    return messages
+    return message
 
 
 def increment_counter(message):
