fingerprinting base case handles empty __dict__

hamilton/caching/fingerprinting.py

@@ -71,7 +71,11 @@ def hash_value(obj, *args, depth=0, **kwargs) -> str:
     if depth > MAX_DEPTH:
         return UNHASHABLE
 
-    if hasattr(obj, "__dict__"):
+    # __dict__ attribute contains the instance attributes of the object.
+    # this is typically sufficient to define the object and its behavior, so it's a good target
+    # for a hash in the default case.
+    # Objects that return an empty dict should be skipped (very odd behavior, happens with pandas type)
+    if getattr(obj, "__dict__", {}) != {}:
         return hash_value(obj.__dict__, depth=depth + 1)
 
     # check if the object comes from a module part of the standard library

tests/caching/test_fingerprinting.py

@@ -23,12 +23,24 @@ def test_hash_no_dict_attribute():
     class Foo:
         __slots__ = ()
 
-        def __init__(self):
-            pass
+    obj = Foo()
+    assert not hasattr(obj, "__dict__")
+
+    fingerprint = fingerprinting.hash_value(obj)
+
+    assert fingerprint == fingerprinting.UNHASHABLE
+
+
+def test_empty_dict_attr_is_unhashable():
+    """Classes with an empty __dict__ can't be hashed during the base case."""
+
+    class Foo: ...  # noqa: E701
 
     obj = Foo()
+    assert obj.__dict__ == {}
+
     fingerprint = fingerprinting.hash_value(obj)
-    assert not hasattr(obj, "__dict__")
+
     assert fingerprint == fingerprinting.UNHASHABLE