diff --git a/modules/openapi-generator/src/main/resources/python/python-experimental/model_templates/methods_setattr_getattr_composed.mustache b/modules/openapi-generator/src/main/resources/python/python-experimental/model_templates/methods_setattr_getattr_composed.mustache
index 9adb2a08a1fb..9420fe1582c7 100644
--- a/modules/openapi-generator/src/main/resources/python/python-experimental/model_templates/methods_setattr_getattr_composed.mustache
+++ b/modules/openapi-generator/src/main/resources/python/python-experimental/model_templates/methods_setattr_getattr_composed.mustache
@@ -41,11 +41,17 @@
         if self._path_to_item:
             path_to_item.extend(self._path_to_item)
         path_to_item.append(name)
-        values = set()
+        values = []
+        # A composed model stores child (oneof/anyOf/allOf) models under
+        # self._var_name_to_model_instances. A named property can exist in
+        # multiple child models. If the property is present in more than one
+        # child model, the value must be the same across all the child models.
         if model_instances:
             for model_instance in model_instances:
                 if name in model_instance._data_store:
-                    values.add(model_instance._data_store[name])
+                    v = model_instance._data_store[name]
+                    if v not in values:
+                        values.append(v)
         len_values = len(values)
         if len_values == 0:
             raise ApiKeyError(
@@ -53,10 +59,10 @@
                 path_to_item
             )
         elif len_values == 1:
-            return list(values)[0]
+            return values[0]
         elif len_values > 1:
             raise ApiValueError(
-                "Values stored for property {0} in {1} difffer when looking "
+                "Values stored for property {0} in {1} differ when looking "
                 "at self and self's composed instances. All values must be "
                 "the same".format(name, type(self).__name__),
                 path_to_item
diff --git a/samples/client/petstore/python-experimental/petstore_api/model_utils.py b/samples/client/petstore/python-experimental/petstore_api/model_utils.py
index eed501c84502..10385c4646d2 100644
--- a/samples/client/petstore/python-experimental/petstore_api/model_utils.py
+++ b/samples/client/petstore/python-experimental/petstore_api/model_utils.py
@@ -274,11 +274,17 @@ def __getattr__(self, name):
         if self._path_to_item:
             path_to_item.extend(self._path_to_item)
         path_to_item.append(name)
-        values = set()
+        values = []
+        # A composed model stores child (oneof/anyOf/allOf) models under
+        # self._var_name_to_model_instances. A named property can exist in
+        # multiple child models. If the property is present in more than one
+        # child model, the value must be the same across all the child models.
         if model_instances:
             for model_instance in model_instances:
                 if name in model_instance._data_store:
-                    values.add(model_instance._data_store[name])
+                    v = model_instance._data_store[name]
+                    if v not in values:
+                        values.append(v)
         len_values = len(values)
         if len_values == 0:
             raise ApiKeyError(
@@ -286,10 +292,10 @@ def __getattr__(self, name):
                 path_to_item
             )
         elif len_values == 1:
-            return list(values)[0]
+            return values[0]
         elif len_values > 1:
             raise ApiValueError(
-                "Values stored for property {0} in {1} difffer when looking "
+                "Values stored for property {0} in {1} differ when looking "
                 "at self and self's composed instances. All values must be "
                 "the same".format(name, type(self).__name__),
                 path_to_item
diff --git a/samples/openapi3/client/petstore/python-experimental/petstore_api/model_utils.py b/samples/openapi3/client/petstore/python-experimental/petstore_api/model_utils.py
index eed501c84502..10385c4646d2 100644
--- a/samples/openapi3/client/petstore/python-experimental/petstore_api/model_utils.py
+++ b/samples/openapi3/client/petstore/python-experimental/petstore_api/model_utils.py
@@ -274,11 +274,17 @@ def __getattr__(self, name):
         if self._path_to_item:
             path_to_item.extend(self._path_to_item)
         path_to_item.append(name)
-        values = set()
+        values = []
+        # A composed model stores child (oneof/anyOf/allOf) models under
+        # self._var_name_to_model_instances. A named property can exist in
+        # multiple child models. If the property is present in more than one
+        # child model, the value must be the same across all the child models.
         if model_instances:
             for model_instance in model_instances:
                 if name in model_instance._data_store:
-                    values.add(model_instance._data_store[name])
+                    v = model_instance._data_store[name]
+                    if v not in values:
+                        values.append(v)
         len_values = len(values)
         if len_values == 0:
             raise ApiKeyError(
@@ -286,10 +292,10 @@ def __getattr__(self, name):
                 path_to_item
             )
         elif len_values == 1:
-            return list(values)[0]
+            return values[0]
         elif len_values > 1:
             raise ApiValueError(
-                "Values stored for property {0} in {1} difffer when looking "
+                "Values stored for property {0} in {1} differ when looking "
                 "at self and self's composed instances. All values must be "
                 "the same".format(name, type(self).__name__),
                 path_to_item