[python] Fall back to wire type for unknown encode

.chronus/changes/python-fallback-wire-type-unknown-encode-2026-1-9-0-0-0.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Fall back to wire type for unknown or unsupported encode

packages/http-client-python/emitter/src/types.ts

@@ -463,18 +463,39 @@ const sdkScalarKindToPythonKind: Record<string, string> = {
 function emitBuiltInType(
   type: SdkBuiltInType | SdkDurationType | SdkDateTimeType,
 ): Record<string, any> {
-  if (type.kind === "duration" && type.encode === "seconds") {
-    return getSimpleTypeResult({
-      type: sdkScalarKindToPythonKind[type.wireType.kind],
-      encode: type.encode,
-    });
-  }
-  if (type.encode === "unixTimestamp") {
-    return getSimpleTypeResult({
-      type: "unixtime",
-      encode: type.encode,
-    });
+  if (type.encode) {
+    if (type.kind === "duration") {
+      if (type.encode === "ISO8601") {
+        return getSimpleTypeResult({
+          type: type.kind,
+          encode: type.encode,
+        });
+      }
+    }
+    if (type.kind === "utcDateTime" || type.kind === "offsetDateTime") {
+      if (type.encode === "unixTimestamp") {
+        return getSimpleTypeResult({
+          type: "unixtime",
+          encode: type.encode,
+        });
+      }
+      if (type.encode === "rfc3339" || type.encode === "rfc7231") {
+        return getSimpleTypeResult({
+          type: type.kind,
+          encode: type.encode,
+        });
+      }
+    }
+
+    // fallback to wire type for unknown or unsupported encode
+    if ("wireType" in type && type.wireType !== undefined) {
+      return getSimpleTypeResult({
+        type: sdkScalarKindToPythonKind[type.wireType.kind] || type.wireType.kind,
+        encode: type.encode,
+      });
+    }
   }
+
   return getSimpleTypeResult({
     type: sdkScalarKindToPythonKind[type.kind] || type.kind, // TODO: switch to kind
     encode: type.encode,