diff --git a/packages/costa/test/plugins/python-simple/__init__.py b/packages/costa/test/plugins/python-simple/__init__.py
index 1e36a5648..ea3b134da 100644
--- a/packages/costa/test/plugins/python-simple/__init__.py
+++ b/packages/costa/test/plugins/python-simple/__init__.py
@@ -2,7 +2,7 @@
 
 def main(input):
   print('hello python!', input)
-  if 'fn1' in input:
+  if input.fn1:
     input.fn1(np.zeros(2))
     input.obj.fn2()