MAINT: dtype.name works for NEP 42 dtypes

numpy/core/_dtype.py

@@ -334,6 +334,8 @@ def _name_includes_bit_suffix(dtype):
     elif dtype.type == np.bool_:
         # implied
         return False
+    elif dtype.type is None:
+        return True
     elif np.issubdtype(dtype, np.flexible) and _isunsized(dtype):
         # unspecified
         return False
@@ -348,7 +350,9 @@ def _name_get(dtype):
         # user dtypes don't promise to do anything special
         return dtype.type.__name__
 
-    if issubclass(dtype.type, np.void):
+    if dtype.kind == '\x00':
+        name = type(dtype).__name__
+    elif issubclass(dtype.type, np.void):
         # historically, void subclasses preserve their name, eg `record64`
         name = dtype.type.__name__
     else:

numpy/core/tests/test_custom_dtypes.py

@@ -45,6 +45,9 @@ def test_repr(self):
         # Check the repr, mainly to cover the code paths:
         assert repr(SF(scaling=1.)) == "_ScaledFloatTestDType(scaling=1.0)"
 
+    def test_dtype_name(self):
+        assert SF(1.).name == "_ScaledFloatTestDType64"
+
     @pytest.mark.parametrize("scaling", [1., -1., 2.])
     def test_sfloat_from_float(self, scaling):
         a = np.array([1., 2., 3.]).astype(dtype=SF(scaling))