API: Disallow DataFrame other for Series flex ops (#62648)

Author: jbrockmendel

doc/source/whatsnew/v3.0.0.rst

@@ -655,6 +655,7 @@ Other API changes
  an empty ``RangeIndex`` or empty ``Index`` with object dtype when determining
  the dtype of the resulting Index (:issue:`60797`)
 - :class:`IncompatibleFrequency` now subclasses ``TypeError`` instead of ``ValueError``. As a result, joins with mismatched frequencies now cast to object like other non-comparable joins, and arithmetic with indexes with mismatched frequencies align (:issue:`55782`)
+- :class:`Series` "flex" methods like :meth:`Series.add` no longer allow passing a :class:`DataFrame` for ``other``; use the DataFrame reversed method instead (:issue:`46179`)
 - :meth:`CategoricalIndex.append` no longer attempts to cast different-dtype indexes to the caller's dtype (:issue:`41626`)
 - :meth:`ExtensionDtype.construct_array_type` is now a regular method instead of a ``classmethod`` (:issue:`58663`)
 - Comparison operations between :class:`Index` and :class:`Series` now consistently return :class:`Series` regardless of which object is on the left or right (:issue:`36759`)

pandas/core/series.py

@@ -6069,6 +6069,12 @@ def _flex_method(self, other, op, *, level=None, fill_value=None, axis: Axis = 0
  result = self._binop(other, op, level=level, fill_value=fill_value)
  result._name = res_name
  return result
+ elif isinstance(other, ABCDataFrame):
+ # GH#46179
+ raise TypeError(
+ f"Series.{op.__name__.strip('_')} does not support a DataFrame "
+ f"`other`. Use df.{op.__name__.strip('_')}(ser) instead."
+ )
  else:
  if fill_value is not None:
  if isna(other):

pandas/tests/series/test_arithmetic.py

@@ -156,6 +156,24 @@ def _check_fill(meth, op, a, b, fill_value=0):
  # should accept axis=0 or axis='rows'
  op(a, b, axis=0)
 
+ def test_flex_disallows_dataframe(self):
+ # GH#46179
+ df = pd.DataFrame(
+ {2010: [1], 2020: [3]},
+ index=pd.MultiIndex.from_product([["a"], ["b"]], names=["scen", "mod"]),
+ )
+
+ ser = Series(
+ [10.0, 20.0, 30.0],
+ index=pd.MultiIndex.from_product(
+ [["a"], ["b"], [0, 1, 2]], names=["scen", "mod", "id"]
+ ),
+ )
+
+ msg = "Series.add does not support a DataFrame `other`"
+ with pytest.raises(TypeError, match=msg):
+ ser.add(df, axis=0)
+
 
 class TestSeriesArithmetic:
  # Some of these may end up in tests/arithmetic, but are not yet sorted