Add LegacyMessageType (#3064)

src/py/flwr/common/__init__.py

@@ -16,6 +16,7 @@
 
 
 from .constant import MessageType as MessageType
+from .constant import MessageTypeLegacy as MessageTypeLegacy
 from .context import Context as Context
 from .date import now as now
 from .grpc import GRPC_MAX_MESSAGE_LENGTH
@@ -85,6 +86,7 @@
     "log",
     "Message",
     "MessageType",
+    "MessageTypeLegacy",
     "Metadata",
     "Metrics",
     "MetricsAggregationFn",

src/py/flwr/common/constant.py

@@ -38,7 +38,7 @@
 
 MESSAGE_TYPE_GET_PROPERTIES = "get_properties"
 MESSAGE_TYPE_GET_PARAMETERS = "get_parameters"
-MESSAGE_TYPE_FIT = "fit"
+MESSAGE_TYPE_FIT = "train"
 MESSAGE_TYPE_EVALUATE = "evaluate"
 
 
@@ -53,6 +53,17 @@ def __new__(cls) -> MessageType:
         raise TypeError(f"{cls.__name__} cannot be instantiated.")
 
 
+class MessageTypeLegacy:
+    """Legacy message type."""
+
+    GET_PROPERTIES = "get_properties"
+    GET_PARAMETERS = "get_parameters"
+
+    def __new__(cls) -> MessageTypeLegacy:
+        """Prevent instantiation."""
+        raise TypeError(f"{cls.__name__} cannot be instantiated.")
+
+
 class SType:
     """Serialisation type."""