Fix typing

src/paho/mqtt/client.py

@@ -583,7 +583,7 @@ def __init__(
         clean_session: bool | None = None,
         userdata: Any = None,
         protocol: int = MQTTv311,
-        transport: str = "tcp",
+        transport: Literal["tcp", "websockets"] = "tcp",
         reconnect_on_failure: bool = True,
         manual_ack: bool = False,
     ) -> None:
@@ -627,8 +627,13 @@ def __init__(
         locally.
 
         """
+        transport = transport.lower()  # type: ignore
+        if transport not in ("websockets", "tcp"):
+            raise ValueError(
+                f'transport must be "websockets" or "tcp", not {transport}')
+
         self._manual_ack = manual_ack
-        self.transport = transport
+        self._transport = transport
         self._protocol = protocol
         self._userdata = userdata
         self._sock: SocketLike | None = None
@@ -790,25 +795,21 @@ def keepalive(self, value: int) -> None:
         self._keepalive = value
 
     @property
-    def transport(self) -> str:
+    def transport(self) -> Literal["tcp", "websockets"]:
         """Transport method used for the connection."""
         return self._transport
 
     @transport.setter
-    def transport(self, value: str) -> None:
+    def transport(self, value: Literal["tcp", "websockets"]) -> None:
         """
         Update transport which should be "tcp" or "websockets".
         This will only be used on future (re)connection. You should probably
         use reconnect() to update the connection if established.
         """
-        if value.lower() not in ("websockets", "tcp"):
-            raise ValueError(
-                f'transport must be "websockets" or "tcp", not {value}')
-
-        self._transport = value.lower()
+        self._transport = value
 
     @property
-    def protocol(self) -> int:
+    def protocol(self) -> MQTTProtocolVersion:
         """Protocol version used (MQTT v3, MQTT v3.11, MQTTv5)"""
         return self.protocol
 
@@ -818,7 +819,7 @@ def connect_timeout(self) -> float:
         return self._connect_timeout
 
     @connect_timeout.setter
-    def connect_timeout(self, value: float):
+    def connect_timeout(self, value: float) -> None:
         "Change connect_timeout for future (re)connection"
         if value <= 0.0:
             raise ValueError("timeout must be a positive number")

src/paho/mqtt/publish.py

@@ -33,6 +33,12 @@
     except ImportError:
         from typing_extensions import NotRequired, Required, TypedDict
 
+    try:
+        from typing import Literal
+    except ImportError:
+        from typing_extensions import Literal  # type: ignore
+
+
 
     class AuthParameter(TypedDict, total=False):
         username: Required[str]
@@ -108,7 +114,7 @@ def multiple(
     auth: AuthParameter | None = None,
     tls: TLSParameter | None = None,
     protocol: int = paho.MQTTv311,
-    transport: str = "tcp",
+    transport: Literal["tcp", "websockets"] = "tcp",
     proxy_args: Any | None = None,
 ) -> None:
     """Publish multiple messages to a broker, then disconnect cleanly.
@@ -231,7 +237,7 @@ def single(
     auth: AuthParameter | None = None,
     tls: TLSParameter | None = None,
     protocol: int = paho.MQTTv311,
-    transport: str = "tcp",
+    transport: Literal["tcp", "websockets"] = "tcp",
     proxy_args: Any | None = None,
 ) -> None:
     """Publish a single message to a broker, then disconnect cleanly.