feat: trait_to_py now handles ObserveHandler

ju/__init__.py

@@ -14,3 +14,4 @@
     model_field_descriptions,  # Extracts a dictionary of field paths & their descriptions from model.
 )
 from ju.viz import model_digraph  # visualize pydantic models
+from ju.traitlets_util import trait_to_py

ju/tests/traitlets_util_test.py

@@ -47,8 +47,9 @@ class Color(enum.Enum):
                 traitlets.Enum,
                 traitlets.CaselessStrEnum,
                 traitlets.FuzzyEnum,
+                traitlets.ObserveHandler,
             ]:
-                trait_instance = traitlet_type(values=['a', 'b', 'c'])
+                trait_instance = traitlet_type(['a', 'b', 'c'])
             elif traitlet_type in {traitlets.List, traitlets.Set}:
                 trait_instance = traitlet_type(one_traitlet_type)
             elif traitlet_type is traitlets.Tuple:

ju/traitlets_util.py

@@ -3,11 +3,14 @@
 import traitlets
 from traitlets import TraitType
 import typing
-from typing import Union, Type
+from typing import Union, Type, Any, Callable, Dict
+
 import enum
 import re
 import collections.abc
 
+ObserveHandlerPyType = Callable[[Dict[str, Any]], Any]
+
 # Mapping from traitlets types to Python types (as defined previously)
 py_type_for_traitlet_type = {
     # C* types before their base types
@@ -45,6 +48,7 @@
     traitlets.ClassBasedTraitType: type,
     # Other types
     traitlets.Callable: collections.abc.Callable,
+    traitlets.ObserveHandler: ObserveHandlerPyType,
     traitlets.UseEnum: enum.Enum,
     traitlets.Union: typing.Union,
     traitlets.Any: object,