BUG: sparse: raise error for array classes, document/test old behavior

scipy/sparse/_base.py

@@ -1505,7 +1505,15 @@ def getrow(self, i):
 
 class sparray:
     """A namespace class to separate sparray from spmatrix"""
-    pass
+
+
+    def __init__(self, *args, **kwargs):
+        if np.isscalar(args[0]):
+            raise ValueError(
+                "scipy sparse array classes do not \
+                    support instantiation from a scalar"
+            )
+        super().__init__(*args, **kwargs)
 
 sparray.__doc__ = _spbase.__doc__
 

scipy/sparse/_bsr.py

@@ -94,8 +94,10 @@ def __init__(self, arg1, shape=None, dtype=None, copy=False, blocksize=None):
                     if not isshape(blocksize):
                         raise ValueError(f'invalid blocksize={blocksize}')
                     if tuple(blocksize) != self.data.shape[1:]:
-                        raise ValueError('mismatching blocksize={} vs {}'.format(
-                            blocksize, self.data.shape[1:]))
+                        raise ValueError(
+                            f'mismatching blocksize={blocksize} \
+                                vs {self.data.shape[1:]}'
+                        )
             else:
                 raise ValueError('unrecognized bsr_array constructor usage')
         else:
@@ -640,7 +642,7 @@ def isspmatrix_bsr(x):
 
 
 # This namespace class separates array from matrix with isinstance
-class bsr_array(_bsr_base, sparray):
+class bsr_array(sparray, _bsr_base):
     """
     Block Sparse Row format sparse array.
 

scipy/sparse/_coo.py

@@ -626,7 +626,7 @@ def isspmatrix_coo(x):
 
 
 # This namespace class separates array from matrix with isinstance
-class coo_array(_coo_base, sparray):
+class coo_array(sparray, _coo_base):
     """
     A sparse array in COOrdinate format.
 

scipy/sparse/_csc.py

@@ -173,7 +173,7 @@ def isspmatrix_csc(x):
 
 
 # This namespace class separates array from matrix with isinstance
-class csc_array(_csc_base, sparray):
+class csc_array(sparray, _csc_base):
     """
     Compressed Sparse Column array.
 

scipy/sparse/_csr.py

@@ -244,7 +244,7 @@ def isspmatrix_csr(x):
 
 
 # This namespace class separates array from matrix with isinstance
-class csr_array(_csr_base, sparray):
+class csr_array(sparray, _csr_base):
     """
     Compressed Sparse Row array.
 

scipy/sparse/_dia.py

@@ -413,7 +413,7 @@ def isspmatrix_dia(x):
 
 
 # This namespace class separates array from matrix with isinstance
-class dia_array(_dia_base, sparray):
+class dia_array(sparray, _dia_base):
     """
     Sparse array with DIAgonal storage.
 

scipy/sparse/_dok.py

@@ -519,7 +519,7 @@ def isspmatrix_dok(x):
 
 
 # This namespace class separates array from matrix with isinstance
-class dok_array(_dok_base, sparray):
+class dok_array(sparray, _dok_base):
     """
     Dictionary Of Keys based sparse array.
 

scipy/sparse/_lil.py

@@ -488,7 +488,7 @@ def isspmatrix_lil(x):
 
 
 # This namespace class separates array from matrix with isinstance
-class lil_array(_lil_base, sparray):
+class lil_array(sparray, _lil_base):
     """
     Row-based LIst of Lists sparse array.
 

scipy/sparse/tests/test_construct.py

@@ -11,7 +11,11 @@
 
 from scipy.sparse import (csr_matrix, coo_matrix,
                           csr_array, coo_array,
-                          sparray, spmatrix,
+                          csc_array, bsr_array,
+                          dia_array, dok_array,
+                          lil_array, csc_matrix,
+                          bsr_matrix, dia_matrix,
+                          lil_matrix, sparray, spmatrix,
                           _construct as construct)
 from scipy.sparse._construct import rand as sprand
 
@@ -37,6 +41,33 @@ def _sprandn_array(m, n, density=0.01, format="coo", dtype=None, random_state=No
 
 
 class TestConstructUtils:
+
+    @pytest.mark.parametrize("cls", [
+        csc_array, csr_array, coo_array, bsr_array,
+        dia_array, dok_array, lil_array
+    ])
+    def test_singleton_array_constructor(self, cls):
+        with pytest.raises(
+            ValueError,
+            match='scipy sparse array classes do not \
+                support instantiation from a scalar'
+        ):
+            cls(0)
+
+    @pytest.mark.parametrize("cls", [
+        csc_matrix, csr_matrix, coo_matrix,
+        bsr_matrix, dia_matrix, lil_matrix
+    ])
+    def test_singleton_matrix_constructor(self, cls):
+        """
+        This test is for backwards compatibility post scipy 1.13.
+        The behavior observed here is what is to be expected
+        with the older matrix classes. This test comes with the
+        exception of dok_matrix, which was not working pre scipy1.12
+        (unlike the rest of these).
+        """
+        assert cls(0).shape == (1, 1)
+
     def test_spdiags(self):
         diags1 = array([[1, 2, 3, 4, 5]])
         diags2 = array([[1, 2, 3, 4, 5],