BUG: raise when doing arithmetic on DataFrame and list of iterables

doc/source/whatsnew/v1.2.0.rst

@@ -494,6 +494,7 @@ Other
 - Fixed metadata propagation in the :class:`Series.dt` and :class:`Series.str` accessors (:issue:`28283`)
 - Bug in :meth:`Index.union` behaving differently depending on whether operand is a :class:`Index` or other list-like (:issue:`36384`)
 - Passing an array with 2 or more dimensions to the :class:`Series` constructor now raises the more specific ``ValueError``, from a bare ``Exception`` previously (:issue:`35744`)
+- Bug in :class:`DataFrame` allowing arithmetic operations with list of array-likes with undefined results. Behavior changed to raising ``ValueError`` (:issue:`36702`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/ops/__init__.py

@@ -13,7 +13,7 @@
 from pandas._typing import Level
 from pandas.util._decorators import Appender
 
-from pandas.core.dtypes.common import is_list_like
+from pandas.core.dtypes.common import is_array_like, is_list_like
 from pandas.core.dtypes.generic import ABCDataFrame, ABCIndexClass, ABCSeries
 from pandas.core.dtypes.missing import isna
 
@@ -311,6 +311,11 @@ def to_series(right):
             )
 
     elif is_list_like(right) and not isinstance(right, (ABCSeries, ABCDataFrame)):
+        # GH 36702. Raise when attempting arithmetic with list of array-like.
+        if any(is_array_like(el) for el in right):
+            raise ValueError(
+                f"Unable to coerce list of {type(right[0])} " "to Series/DataFrame"
+            )
         # GH17901
         right = to_series(right)
 

pandas/tests/frame/test_arithmetic.py

@@ -1577,3 +1577,13 @@ def test_arith_reindex_with_duplicates():
     result = df1 + df2
     expected = pd.DataFrame([[np.nan, 0, 0]], columns=["first", "second", "second"])
     tm.assert_frame_equal(result, expected)
+
+
+def test_arith_list_of_arraylike_raise():
+    # GH 36702. Raise when trying to add list of array-like to DataFrame
+    df = pd.DataFrame({"x": [1, 2], "y": [1, 2]})
+    ser = pd.Series([1, 1])
+
+    msg = f"Unable to coerce list of {type(ser)} to Series/DataFrame"
+    with pytest.raises(ValueError, match=msg):
+        df + [ser, ser]