diff --git a/implementations/python/preserves/schema.py b/implementations/python/preserves/schema.py
index e6d0d5d..37625b6 100644
--- a/implementations/python/preserves/schema.py
+++ b/implementations/python/preserves/schema.py
@@ -360,6 +360,10 @@ class Compiler:
             c._set_schema(self.root, module_path, n, d, None, None)
             ns[n] = c
 
+# a decorator
+def extend(cls):
+    return lambda f: setattr(cls, f.__name__, f)
+
 if __name__ == '__main__':
     c = Compiler()
     schema_bin_filename = pathlib.Path(__file__).parent / '../../../schema/schema.bin'
@@ -368,10 +372,11 @@ if __name__ == '__main__':
         x = Decoder(f.read()).next()
     print(c.root.schema.Schema.decode(x))
 
-    def m(self, x):
+    @extend(c.root.schema.Schema)
+    def f(self, x):
         return ['yay', self.embeddedType, x]
-    c.root.schema.Schema.f = m
     print(c.root.schema.Schema.decode(x).f(123))
+    print(f)
 
     print()