fix: Use the string representation of a Python UDF as its name when i…

…t doesn't have the __name__ attribute (#6399)

Fixes #6397

engine/table/src/main/java/io/deephaven/engine/util/PyCallableWrapperJpyImpl.java

@@ -302,7 +302,12 @@ public void verifyArguments(Class<?>[] argTypes) {
             return;
         }
 
-        String callableName = pyCallable.getAttribute("__name__").toString();
+        String callableName;
+        if (pyCallable.hasAttribute("__name__")) {
+            callableName = pyCallable.getAttribute("__name__").toString();
+        } else {
+            callableName = pyCallable.toString();
+        }
         List<Parameter> parameters = signature.getParameters();
 
         if (parameters.size() == 0 && argTypes.length > 0) {

py/server/tests/test_udf_scalar_args.py

@@ -619,6 +619,17 @@ def test_no_signature(self):
         self.assertEqual(t.columns[0].data_type, dtypes.int32)
         self.assertEqual(10, t.to_string().count("3"))
 
+    def test_no_name(self):
+        from functools import partial
+        def fn(i: int, z: int) -> int:
+            return i * 5 - z
+        local_fn = partial(fn, z=5)
+
+        t = empty_table(5).update("col=i*2")
+        t = t.update('col2=local_fn(col)')
+        self.assertEqual(t.columns[1].data_type, dtypes.int64)
+        self.assertEqual(5, t.size)
+
 
 if __name__ == "__main__":
     unittest.main()