Add note instead of catching and raising unhashable exception

pydra/engine/specs.py

@@ -999,9 +999,9 @@ def get_value(
                 "that don't return stable hash values for specific object "
                 "types across multiple processes (see bytes_repr() "
                 '"singledispatch "function in pydra/utils/hash.py).'
-                "You may need to implement a specific `bytes_repr()` "
-                '"singledispatch overload"s or `__bytes_repr__()` '
-                "dunder methods to handle one or more types in "
+                "You may need to write specific `bytes_repr()` "
+                "implementations (see `pydra.utils.hash.register_serializer`) or a "
+                "`__bytes_repr__()` dunder methods to handle one or more types in "
                 "your interface inputs."
             )
         _, split_depth = TypeParser.strip_splits(self.type)

pydra/engine/submitter.py

@@ -228,10 +228,10 @@ async def expand_workflow(self, wf, rerun=False):
                                 "that don't return stable hash values for specific object "
                                 "types across multiple processes (see bytes_repr() "
                                 '"singledispatch "function in pydra/utils/hash.py).'
-                                "You may need to implement a specific `bytes_repr()` "
-                                '"singledispatch overload"s or `__bytes_repr__()` '
-                                "dunder methods to handle one or more types in "
-                                "your interface inputs."
+                                "You may need to write specific `bytes_repr()` "
+                                "implementations (see `pydra.utils.hash.register_serializer`) "
+                                "or `__bytes_repr__()` dunder methods to handle one "
+                                "or more types in your interface inputs."
                             )
                         raise RuntimeError(msg)
             for task in tasks:

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 +220,17 @@ 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
+        tp = type(obj)
+        add_exc_note(
+            e,
+            (
+                f"and therefore cannot hash `{obj!r}` of type "
+                f"`{tp.__module__}.{tp.__name__}`. Consider implementing a "
+                "specific `bytes_repr()`(see pydra.utils.hash.register_serializer) "
+                "or a `__bytes_repr__()` dunder methods for this type"
+            ),
+        )
+        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,
@@ -386,3 +385,28 @@ def test_persistent_hash_cache_not_dir(text_file):
     """
     with pytest.raises(ValueError, match="is not a directory"):
         PersistentCache(text_file.fspath)
+
+
+def test_unhashable():
+    """
+    Test that an error is raised if an unhashable object is provided
+    """
+
+    class A:
+
+        def __bytes_repr__(self, cache: Cache) -> ty.Generator[bytes, None, None]:
+            raise TypeError("unhashable")
+
+        def __repr__(self):
+            return "A()"
+
+    # hash_object(A())
+
+    with pytest.raises(
+        TypeError,
+        match=(
+            "unhashable\nand therefore cannot hash `A\(\)` of type "
+            "`pydra.utils.tests.test_hash.A`"
+        ),
+    ):
+        hash_object(A())