--- /dev/null
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements. See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License. You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from aria.utils.caching import cachedmethod
+from aria.parser.presentation import (Presentation, has_fields, primitive_dict_field)
+
+
+@has_fields
+class ExtensiblePresentation(Presentation):
+ """
+ A presentation that supports an optional ``_extensions`` dict field.
+ """
+
+ @primitive_dict_field()
+ def _extensions(self):
+ pass
+
+ @cachedmethod
+ def _get_extension(self, name, default=None):
+ extensions = self._extensions
+ return extensions.get(name, default) if extensions is not None else None # pylint: disable=no-member