diff --git a/features/activity/cancel_try_cancel/feature.py b/features/activity/cancel_try_cancel/feature.py
index 603ffcb7..0c67d514 100644
--- a/features/activity/cancel_try_cancel/feature.py
+++ b/features/activity/cancel_try_cancel/feature.py
@@ -66,9 +66,9 @@ async def cancellable_activity() -> None:
         result = "cancelled"
 
     # Send result as signal to workflow
-    await client.get_workflow_handle_for(
-        Workflow.run, activity.info().workflow_id or ""
-    ).signal(Workflow.activity_result, result)
+    await client.get_workflow_handle(activity.info().workflow_id or "").signal(
+        Workflow.activity_result, result
+    )
 
 
 async def start(runner: Runner) -> WorkflowHandle:
diff --git a/features/continue_as_new/continue_as_same/feature.py b/features/continue_as_new/continue_as_same/feature.py
index 86cead00..78e42314 100644
--- a/features/continue_as_new/continue_as_same/feature.py
+++ b/features/continue_as_new/continue_as_same/feature.py
@@ -22,9 +22,9 @@ async def run(self, input: str) -> str:
 
 async def start(runner: Runner) -> WorkflowHandle:
     return await runner.client.start_workflow(
-        Workflow,
+        Workflow.run,
+        INPUT_DATA,
         id=WORKFLOW_ID,
-        arg=INPUT_DATA,
         memo={
             MEMO_KEY: MEMO_VALUE,
         },
diff --git a/features/signal/basic/feature.py b/features/signal/basic/feature.py
index 13b2d6df..2a6ed2e4 100644
--- a/features/signal/basic/feature.py
+++ b/features/signal/basic/feature.py
@@ -22,8 +22,8 @@ async def my_signal(self, arg: str):
 
 
 async def start(runner: Runner) -> WorkflowHandle:
-    handle: WorkflowHandle = await runner.client.start_workflow(
-        Workflow,
+    handle = await runner.client.start_workflow(
+        Workflow.run,
         id="workflow-id",
         task_queue=runner.task_queue,
         execution_timeout=timedelta(minutes=1),
diff --git a/sdkbuild/python.go b/sdkbuild/python.go
index 7dc03296..6a2b2675 100644
--- a/sdkbuild/python.go
+++ b/sdkbuild/python.go
@@ -114,6 +114,19 @@ requires-python = "~=3.10"
 	if err := executeCommand("uv", "sync"); err != nil {
 		return nil, fmt.Errorf("failed installing: %w", err)
 	}
+	// Install mypy for type checking
+	if err := executeCommand("uv", "add", "--dev", "mypy"); err != nil {
+		return nil, fmt.Errorf("failed installing mypy: %w", err)
+	}
+	
+	// Create __init__.py files in feature directories to make them proper Python packages
+	if err := executeCommand("find", "../features", "-type", "d", "-exec", "touch", "{}/__init__.py", ";"); err != nil {
+		return nil, fmt.Errorf("failed creating __init__.py files: %w", err)
+	}
+	
+	if err := executeCommand("uv", "run", "mypy", "--explicit-package-bases", "../features"); err != nil {
+		return nil, fmt.Errorf("failed type checking: %w", err)
+	}
 
 	success = true
 	return &PythonProgram{dir}, nil