Use structural typing for the interface

Author: dandavison

temporalio/client.py

@@ -66,7 +66,6 @@
 from temporalio.converter import (
     DataConverter,
     SerializationContext,
-    WithSerializationContext,
     WorkflowSerializationContext,
 )
 from temporalio.service import (
@@ -2737,7 +2736,7 @@ class AsyncActivityIDReference:
     activity_id: str
 
 
-class AsyncActivityHandle(WithSerializationContext):
+class AsyncActivityHandle:
     """Handle representing an external activity for completion and heartbeat."""
 
     def __init__(

temporalio/converter.py

@@ -28,13 +28,15 @@
     Mapping,
     NewType,
     Optional,
+    Protocol,
     Sequence,
     Tuple,
     Type,
     TypeVar,
     Union,
     get_type_hints,
     overload,
+    runtime_checkable,
 )
 
 import google.protobuf.duration_pb2
@@ -136,10 +138,13 @@ class ActivitySerializationContext(BaseWorkflowSerializationContext):
     is_local: bool
 
 
-# TODO: duck typing or nominal typing?
-class WithSerializationContext(ABC):
+@runtime_checkable
+class WithSerializationContext(Protocol):
     """Interface for classes that can use serialization context.
 
+    To use serialization context in your class, implementing this interface is sufficient; you do
+    not need to inherit from this class.
+
     The following classes may implement this interface:
     - :py:class:`PayloadConverter`
     - :py:class:`PayloadCodec`
@@ -331,7 +336,7 @@ def from_payload(
         raise NotImplementedError
 
 
-class CompositePayloadConverter(PayloadConverter, WithSerializationContext):
+class CompositePayloadConverter(PayloadConverter):
     """Composite payload converter that delegates to a list of encoding payload converters.
 
     Encoding/decoding are attempted on each payload converter successively until

tests/test_serialization_context.py

@@ -38,7 +38,6 @@
     PayloadCodec,
     PayloadConverter,
     SerializationContext,
-    WithSerializationContext,
     WorkflowSerializationContext,
 )
 from temporalio.exceptions import ApplicationError
@@ -66,9 +65,7 @@ class TraceData:
     items: list[TraceItem] = field(default_factory=list)
 
 
-class SerializationContextPayloadConverter(
-    EncodingPayloadConverter, WithSerializationContext
-):
+class SerializationContextPayloadConverter(EncodingPayloadConverter):
     def __init__(self):
         self.context: Optional[SerializationContext] = None
 
@@ -133,9 +130,7 @@ def from_payload(
         return value
 
 
-class SerializationContextCompositePayloadConverter(
-    CompositePayloadConverter, WithSerializationContext
-):
+class SerializationContextCompositePayloadConverter(CompositePayloadConverter):
     def __init__(self):
         super().__init__(
             SerializationContextPayloadConverter(),
@@ -1000,7 +995,7 @@ async def run(self) -> Never:
 test_traces: dict[str, list[TraceItem]] = defaultdict(list)
 
 
-class FailureConverterWithContext(DefaultFailureConverter, WithSerializationContext):
+class FailureConverterWithContext(DefaultFailureConverter):
     def __init__(self):
         super().__init__(encode_common_attributes=False)
         self.context: Optional[SerializationContext] = None
@@ -1131,7 +1126,7 @@ async def test_failure_converter_with_context(client: Client):
 # Test payload codec
 
 
-class PayloadCodecWithContext(PayloadCodec, WithSerializationContext):
+class PayloadCodecWithContext(PayloadCodec):
     def __init__(self):
         self.context: Optional[SerializationContext] = None
         self.encode_called_with_context = False
@@ -1432,7 +1427,7 @@ async def test_child_workflow_codec_with_context(client: Client):
 # Payload codec: test decode context matches encode context
 
 
-class PayloadEncryptionCodec(PayloadCodec, WithSerializationContext):
+class PayloadEncryptionCodec(PayloadCodec):
     """
     The outbound data for encoding must always be the string "outbound". "Encrypt" it by replacing
     it with a key that is derived from the context available during encoding. On decryption, assert
@@ -1597,7 +1592,7 @@ async def test_decode_context_matches_encode_context(
 # Test nexus payload codec
 
 
-class AssertNexusLacksContextPayloadCodec(PayloadCodec, WithSerializationContext):
+class AssertNexusLacksContextPayloadCodec(PayloadCodec):
     def __init__(self):
         self.context = None
 
@@ -1679,9 +1674,7 @@ class PydanticData(BaseModel):
     trace: List[str] = []
 
 
-class PydanticJSONConverterWithContext(
-    PydanticJSONPlainPayloadConverter, WithSerializationContext
-):
+class PydanticJSONConverterWithContext(PydanticJSONPlainPayloadConverter):
     def __init__(self):
         super().__init__()
         self.context: Optional[SerializationContext] = None
@@ -1700,7 +1693,7 @@ def to_payload(self, value: Any) -> Optional[temporalio.api.common.v1.Payload]:
         return super().to_payload(value)
 
 
-class PydanticConverterWithContext(CompositePayloadConverter, WithSerializationContext):
+class PydanticConverterWithContext(CompositePayloadConverter):
     def __init__(self):
         super().__init__(
             *(
@@ -1758,9 +1751,7 @@ class UserMethodCalledError(Exception):
     pass
 
 
-class CustomEncodingPayloadConverter(
-    JSONPlainPayloadConverter, WithSerializationContext
-):
+class CustomEncodingPayloadConverter(JSONPlainPayloadConverter):
     @property
     def encoding(self) -> str:
         return "custom-encoding-that-does-not-clash-with-default-converters"