DEPR: SparseArray(scalar) (pandas-dev#53039)

* DEPR: SparseArray(scalar)

* Update doc/source/whatsnew/v2.1.0.rst

Co-authored-by: Matthew Roeschke <[email protected]>

---------

Co-authored-by: Matthew Roeschke <[email protected]>

Author: 2 people

doc/source/whatsnew/v2.1.0.rst

@@ -259,6 +259,8 @@ Deprecations
 - Deprecated unused "closed" and "normalize" keywords in the :class:`DatetimeIndex` constructor (:issue:`52628`)
 - Deprecated unused "closed" keyword in the :class:`TimedeltaIndex` constructor (:issue:`52628`)
 - Deprecated logical operation between two non boolean :class:`Series` with different indexes always coercing the result to bool dtype. In a future version, this will maintain the return type of the inputs. (:issue:`52500`, :issue:`52538`)
+- Deprecated constructing :class:`SparseArray` from scalar data, pass a sequence instead (:issue:`53039`)
+-
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_210.performance:

pandas/core/arrays/sparse/array.py

@@ -398,6 +398,12 @@ def __init__(
             dtype = dtype.subtype
 
         if is_scalar(data):
+            warnings.warn(
+                f"Constructing {type(self).__name__} with scalar data is deprecated "
+                "and will raise in a future version. Pass a sequence instead.",
+                FutureWarning,
+                stacklevel=find_stack_level(),
+            )
             if sparse_index is None:
                 npoints = 1
             else:

pandas/tests/arrays/sparse/test_constructors.py

@@ -145,13 +145,16 @@ def test_constructor_spindex_dtype(self):
     @pytest.mark.parametrize("sparse_index", [None, IntIndex(1, [0])])
     def test_constructor_spindex_dtype_scalar(self, sparse_index):
         # scalar input
-        arr = SparseArray(data=1, sparse_index=sparse_index, dtype=None)
+        msg = "Constructing SparseArray with scalar data is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            arr = SparseArray(data=1, sparse_index=sparse_index, dtype=None)
         exp = SparseArray([1], dtype=None)
         tm.assert_sp_array_equal(arr, exp)
         assert arr.dtype == SparseDtype(np.int64)
         assert arr.fill_value == 0
 
-        arr = SparseArray(data=1, sparse_index=IntIndex(1, [0]), dtype=None)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            arr = SparseArray(data=1, sparse_index=IntIndex(1, [0]), dtype=None)
         exp = SparseArray([1], dtype=None)
         tm.assert_sp_array_equal(arr, exp)
         assert arr.dtype == SparseDtype(np.int64)