add note instead of catching and raising unhashable exception

Author: tclose

pydra/utils/__init__.py

@@ -1,11 +1 @@
-from pathlib import Path
-import platformdirs
-from pydra._version import __version__
-
-user_cache_dir = Path(
-    platformdirs.user_cache_dir(
-        appname="pydra",
-        appauthor="nipype",
-        version=__version__,
-    )
-)
+from .misc import user_cache_dir, add_exc_note  # noqa: F401

pydra/utils/hash.py

@@ -19,7 +19,7 @@
 from filelock import SoftFileLock
 import attrs.exceptions
 from fileformats.core import FileSet
-from . import user_cache_dir
+from . import user_cache_dir, add_exc_note
 
 logger = logging.getLogger("pydra")
 
@@ -197,10 +197,6 @@ def __contains__(self, object_id):
         return object_id in self._hashes
 
 
-class UnhashableError(ValueError):
-    """Error for objects that cannot be hashed"""
-
-
 def hash_function(obj, **kwargs):
     """Generate hash of object."""
     return hash_object(obj, **kwargs).hex()
@@ -224,7 +220,8 @@ def hash_object(
     try:
         return hash_single(obj, cache)
     except Exception as e:
-        raise UnhashableError(f"Cannot hash object {obj!r} due to '{e}'") from e
+        add_exc_note(e, f"Therefore cannot hash object {obj!r}")
+        raise e
 
 
 def hash_single(obj: object, cache: Cache) -> Hash:

pydra/utils/misc.py

@@ -0,0 +1,33 @@
+from pathlib import Path
+import platformdirs
+from pydra._version import __version__
+
+user_cache_dir = Path(
+    platformdirs.user_cache_dir(
+        appname="pydra",
+        appauthor="nipype",
+        version=__version__,
+    )
+)
+
+
+def add_exc_note(e: Exception, note: str) -> Exception:
+    """Adds a note to an exception in a Python <3.11 compatible way
+
+    Parameters
+    ----------
+    e : Exception
+        the exception to add the note to
+    note : str
+        the note to add
+
+    Returns
+    -------
+    Exception
+        returns the exception again
+    """
+    if hasattr(e, "add_note"):
+        e.add_note(note)
+    else:
+        e.args = (e.args[0] + "\n" + note,)
+    return e

pydra/utils/tests/test_hash.py

@@ -11,7 +11,6 @@
 from fileformats.text import TextFile
 from ..hash import (
     Cache,
-    UnhashableError,
     bytes_repr,
     hash_object,
     register_serializer,