it seems we cannot combine required fields in subclass with superclass having optional ones when using dataclasses

Author: rambo

src/scpi/transports/gpib/prologix.py

@@ -21,8 +21,8 @@ class PrologixRS232SerialProtocol(RS232SerialProtocol):
     TERMINATOR = b"\n"
 
 
-@dataclass  # type ignored to workaround nondefault cannot follow default
-class PrologixGPIBTransport(GPIBTransport, RS232Transport):  # type: ignore
+@dataclass
+class PrologixGPIBTransport(GPIBTransport, RS232Transport):
     """Transport "driver" for the Prologix USB-GPIB controller (v6 protocol)"""
 
     def __post_init__(self) -> None:

src/scpi/transports/rs232.py

@@ -33,11 +33,13 @@ def handle_line(self, line: str) -> None:
 class RS232Transport(BaseTransport):
     """Uses PySerials ReaderThread in the background to save us some pain"""
 
-    serialdevice: serial.SerialBase = field(repr=True)  # type: ignore # workaround nondefault cannot follow default
+    serialdevice: Optional[serial.SerialBase] = field(default=None)
     _serialhandler: Optional[serial.threaded.ReaderThread] = field(default=None, repr=False)
 
     def __post_init__(self) -> None:
         """Initialize the transport"""
+        if not self.serialdevice:
+            raise ValueError("serialdevice must be given")
         self._serialhandler = serial.threaded.ReaderThread(self.serialdevice, RS232SerialProtocol)
         self._serialhandler.start()
         self._serialhandler.protocol.handle_line = self.message_received

src/scpi/transports/tcp.py

@@ -15,8 +15,8 @@
 class TCPTransport(BaseTransport):
     """TCP based transport"""
 
-    ipaddr: str = field()  # type: ignore # workaround nondefault cannot follow default
-    port: int = field()  # type: ignore # workaround nondefault cannot follow default
+    ipaddr: Optional[str] = field(default=None)
+    port: Optional[int] = field(default=None)
     reader: Optional[asyncio.StreamReader] = field(default=None)
     writer: Optional[asyncio.StreamWriter] = field(default=None)
 
@@ -28,6 +28,8 @@ async def open_connection(self, ipaddr: str, port: int) -> None:
 
     def __post_init__(self) -> None:
         """Call open_connection in an eventloop"""
+        if self.ipaddr is None or self.port is None:
+            raise ValueError("ipaddr and port must be given")
         loop = asyncio.get_event_loop()
         loop.run_until_complete(self.open_connection(self.ipaddr, self.port))