Check easily made user mistake for count_ etc. (#4590)

py/server/deephaven/agg.py

@@ -106,6 +106,8 @@ def count_(col: str) -> Aggregation:
     Returns:
         an aggregation
     """
+    if not isinstance(col, str):
+        raise DHError(message="count_ aggregation requires a string value for the 'col' argument.")
     return Aggregation(j_aggregation=_JAggregation.AggCount(col))
 
 
@@ -119,6 +121,8 @@ def partition(col: str, include_by_columns: bool = True) -> Aggregation:
     Returns:
         an aggregation
     """
+    if not isinstance(col, str):
+        raise DHError(message="partition aggregation requires a string value for the 'col' argument.")
     return Aggregation(j_aggregation=_JAggregation.AggPartition(col, include_by_columns))
 
 

py/server/tests/test_table.py

@@ -1053,6 +1053,16 @@ def test_has_columns(self):
         self.assertFalse(t.has_columns("D"))
         self.assertFalse(t.has_columns(["D", "C"]))
 
+    def test_agg_count_and_partition_error(self):
+        t = empty_table(1).update(["A=i", "B=i", "C=i"])
+        with self.assertRaises(DHError) as cm:
+            t.agg_by(aggs=count_(["A"]), by=["B"])
+        self.assertIn("string value", str(cm.exception))
+
+        with self.assertRaises(DHError) as cm:
+            t.agg_by(aggs=[partition(["A"])], by=["B"])
+        self.assertIn("string value", str(cm.exception))
+
 
 if __name__ == "__main__":
     unittest.main()