[python-experimental] implement in operator for model classes (#7637)

* implement  operator for model classes

* refresh samples

modules/openapi-generator/src/main/resources/python/python-experimental/model_templates/methods_setattr_getattr_composed.mustache

@@ -68,4 +68,20 @@
                 "at self and self's composed instances. All values must be "
                 "the same".format(name, type(self).__name__),
                 path_to_item
-            )
+            )
+
+    def __contains__(self, name):
+        """this allows us to use `in` operator: `'attr' in instance`"""
+
+        if name in self.required_properties:
+            return name in self.__dict__
+
+        model_instances = self._var_name_to_model_instances.get(
+            name, self._additional_properties_model_instances)
+
+        if model_instances:
+            for model_instance in model_instances:
+                if name in model_instance._data_store:
+                    return True
+
+        return False

modules/openapi-generator/src/main/resources/python/python-experimental/model_templates/methods_setattr_getattr_normal.mustache

@@ -22,4 +22,11 @@
             "{0} has no attribute '{1}'".format(
                 type(self).__name__, name),
             [name]
-        )
+        )
+
+    def __contains__(self, name):
+        """this allows us to use `in` operator: `'attr' in instance`"""
+        if name in self.required_properties:
+            return name in self.__dict__
+
+        return name in self.__dict__['_data_store']