BUG/ERR: sparse array cmp methods mismatched len (pandas-dev#43863)

Author: mzeitlin11

doc/source/whatsnew/v1.4.0.rst

@@ -511,6 +511,7 @@ Sparse
 - Bug in :meth:`DataFrame.sparse.to_coo` raising ``AttributeError`` when column names are not unique (:issue:`29564`)
 - Bug in :meth:`SparseArray.max` and :meth:`SparseArray.min` raising ``ValueError`` for arrays with 0 non-null elements (:issue:`43527`)
 - Bug in :meth:`DataFrame.sparse.to_coo` silently converting non-zero fill values to zero (:issue:`24817`)
+- Bug in :class:`SparseArray` comparison methods with an array-like operand of mismatched length raising ``AssertionError`` or unclear ``ValueError`` depending on the input (:issue:`43863`)
 -
 
 ExtensionArray

pandas/core/arrays/sparse/array.py

@@ -1642,11 +1642,14 @@ def _cmp_method(self, other, op) -> SparseArray:
 
         if isinstance(other, np.ndarray):
             # TODO: make this more flexible than just ndarray...
-            if len(self) != len(other):
-                raise AssertionError(f"length mismatch: {len(self)} vs. {len(other)}")
             other = SparseArray(other, fill_value=self.fill_value)
 
         if isinstance(other, SparseArray):
+            if len(self) != len(other):
+                raise ValueError(
+                    f"operands have mismatched length {len(self)} and {len(other)}"
+                )
+
             op_name = op.__name__.strip("_")
             return _sparse_array_op(self, other, op, op_name)
         else:

pandas/tests/arrays/sparse/test_arithmetics.py

@@ -529,3 +529,11 @@ def test_unary_op(op, fill_value):
     result = op(sparray)
     expected = SparseArray(op(arr), fill_value=op(fill_value))
     tm.assert_sp_array_equal(result, expected)
+
+
+@pytest.mark.parametrize("cons", [list, np.array, SparseArray])
+def test_mismatched_length_cmp_op(cons):
+    left = SparseArray([True, True])
+    right = cons([True, True, True])
+    with pytest.raises(ValueError, match="operands have mismatched length"):
+        left & right