Update slcan.py

Added additional parameter "listen_only" to open interface/channel with "L" command (in opposite to "O" command).

Author: wolfraven

can/interfaces/slcan.py

@@ -64,6 +64,7 @@ def __init__(
         btr: Optional[str] = None,
         sleep_after_open: float = _SLEEP_AFTER_SERIAL_OPEN,
         rtscts: bool = False,
+        listen_only: bool = False,
         **kwargs: Any,
     ) -> None:
         """
@@ -82,11 +83,16 @@ def __init__(
             Time to wait in seconds after opening serial connection
         :param rtscts:
             turn hardware handshake (RTS/CTS) on and off
+        :param listen_only:
+            If True, open interface/channel in listen mode with ``L`` command.
+            Otherwise the (default) ``O`` command is still used. See ``open`` methode. 
 
         :raise ValueError: if both ``bitrate`` and ``btr`` are set or the channel is invalid
         :raise CanInterfaceNotImplementedError: if the serial module is missing
         :raise CanInitializationError: if the underlying serial connection could not be established
         """
+        self.listen_only = listen_only
+        
         if serial is None:
             raise CanInterfaceNotImplementedError("The serial module is not installed")
 
@@ -192,7 +198,10 @@ def flush(self) -> None:
                 self.serialPortOrig.read()
 
     def open(self) -> None:
-        self._write("O")
+        if self.listen_only == True:
+            self._write("L")
+        else:
+            self._write("O")
 
     def close(self) -> None:
         self._write("C")