simpleflow classes support

patch.diff

diff --git a/examples/basic.py b/examples/basic.py
index 1b5e538..f431c59 100644
--- a/examples/basic.py
+++ b/examples/basic.py
@@ -17,10 +17,18 @@ def double(x):
     return x * 2
 
 
+# simpleflow activities can be classes ; in that case the class is instantiated
+# with the params passed via submit, then the `execute()` method is called and
+# the result is returned.
 @activity.with_attributes(task_list='quickstart', version='example')
-def delay(t, x):
-    time.sleep(t)
-    return x
+class Delay(object):
+    def __init__(self, t, x):
+        self.t = t
+        self.x = x
+
+    def execute(self):
+        time.sleep(self.t)
+        return self.x
 
 
 class BasicWorkflow(Workflow):
@@ -30,7 +38,7 @@ class BasicWorkflow(Workflow):
 
     def run(self, x, t=30):
         y = self.submit(increment, x)
-        yy = self.submit(delay, t, y)
+        yy = self.submit(Delay, t, y)
         z = self.submit(double, y)
 
         print '({x} + 1) * 2 = {result}'.format(
diff --git a/simpleflow/local/executor.py b/simpleflow/local/executor.py
index 0f81983..734ac11 100644
--- a/simpleflow/local/executor.py
+++ b/simpleflow/local/executor.py
@@ -23,8 +23,12 @@ class Executor(executor.Executor):
                   key, val in kwargs.iteritems()}
 
         future = futures.Future()
+        handler = func._callable
         try:
-            future._result = func._callable(*args, **kwargs)
+            if hasattr(handler, 'execute'):
+                future._result = handler(*args, **kwargs).execute()
+            else:
+                future._result = handler(*args, **kwargs)
         except Exception as err:
             future._exception = err
             if func.raises_on_failure:
diff --git a/simpleflow/swf/process/worker/base.py b/simpleflow/swf/process/worker/base.py
index b45e1bb..57afe70 100644
--- a/simpleflow/swf/process/worker/base.py
+++ b/simpleflow/swf/process/worker/base.py
@@ -106,7 +106,10 @@ class ActivityWorker(object):
         args = input.get('args', ())
         kwargs = input.get('kwargs', {})
         try:
-            result = handler(*args, **kwargs)
+            if hasattr(handler, 'execute'):
+                result = handler(*args, **kwargs).execute()
+            else:
+                result = handler(*args, **kwargs)
         except Exception as err:
             tb = traceback.format_exc()
             logger.exception(err)