Fix ParamDict dunder attributes

CHANGELOG.md

@@ -7,6 +7,13 @@ project adheres to clauses 1–8 of [Semantic Versioning](https://semver.org/spe
 
 ## [Unreleased]
 
+## [0.15.1] (Jun 25 2024)
+
+### Fixed
+
+- `ParamDict` treats dunder names (e.g. `__init__`) as attributes, allowing internal
+  Python functionalities to work.
+
 ## [0.15.0] (Jun 21 2024)
 
 ### Added

paramdb/_param_data/_collections.py

@@ -210,8 +210,8 @@ def __delattr__(self, name: str) -> None:
 
     def _is_attribute(self, name: str) -> bool:
         """
-        If the given name matches an existing attribute or has a corresponding class
-        type hint, treat it as the name of an attribute.
+        If the given name matches an existing attribute, has a corresponding class type
+        hint, or is a dunder name (e.g. __init__), treat it as the name of an attribute.
         """
         try:
             self.__getattribute__(name)  # pylint: disable=unnecessary-dunder-call
@@ -221,4 +221,5 @@ def _is_attribute(self, name: str) -> bool:
         class_annotations: dict[str, Any] = {}
         for cls in type(self).mro():
             class_annotations |= getattr(cls, "__annotations__", {})
-        return existing_attribute or name in class_annotations
+        dunder = name.startswith("__") and name.endswith("__")
+        return existing_attribute or name in class_annotations or dunder