Better error message for edc.AutoCast assignement

PiperOrigin-RevId: 581914801

etils/edc/field_utils.py

@@ -20,6 +20,8 @@
 import typing
 from typing import Any, Callable, Generic, Optional, Type, TypeVar
 
+from etils import epy
+
 _Dataclass = Any
 _In = Any
 _Out = Any
@@ -69,7 +71,7 @@ def __init__(
     self._attribute_name: Optional[str] = None
     self._objtype: Optional[Type[_Dataclass]] = None
 
-    self._validate = validate
+    self._validate_fn = validate
     self._field_kwargs = field_kwargs
 
     # Whether `__get__` has not been called yet. See `__get__` for details.
@@ -115,6 +117,12 @@ def __set__(self, obj: _Dataclass, value: _InT) -> None:
     # Validate the value during assignement
     _setattr(obj, self._attribute_name, self._validate(value))
 
+  def _validate(self, value: _InT) -> _OutT:
+    try:
+      return self._validate_fn(value)
+    except Exception as e:  # pylint: disable=broad-exception-caught
+      epy.reraise(e, prefix=f'Error assigning {self._attribute_name!r}: ')
+
 
 # Because there is one instance of the `_Field` per class, shared across all
 # class instances, we need to store the per-object state somewhere.