test_numpy_dtypes: Show conversion btw cls and np.dtype / np.generic

Author: EricCousineau-TRI

tests/test_numpy_dtypes.cpp

@@ -259,7 +259,26 @@ TEST_SUBMODULE(numpy_dtypes, m) {
     catch (...) { return; }
 
     // typeinfo may be registered before the dtype descriptor for scalar casts to work...
-    py::class_<SimpleStruct>(m, "SimpleStruct");
+    py::class_<SimpleStruct>(m, "SimpleStruct")
+        // Explicit construct with braces to ensure zero-valued initialization.
+        .def(py::init([]() { return SimpleStruct{}; }))
+        .def_readwrite("bool_", &SimpleStruct::bool_)
+        .def_readwrite("uint_", &SimpleStruct::uint_)
+        .def_readwrite("float_", &SimpleStruct::float_)
+        .def_readwrite("ldbl_", &SimpleStruct::ldbl_)
+        .def("astuple", [](const SimpleStruct& self) {
+            return py::make_tuple(self.bool_, self.uint_, self.float_, self.ldbl_);
+        })
+        .def_static("fromtuple", [](const py::tuple tup) {
+            if (py::len(tup) != 4) {
+                throw py::cast_error("Invalid size");
+            }
+            return SimpleStruct{
+                tup[0].cast<bool>(),
+                tup[1].cast<uint32_t>(),
+                tup[2].cast<float>(),
+                tup[3].cast<long double>()};
+        });
 
     PYBIND11_NUMPY_DTYPE(SimpleStruct, bool_, uint_, float_, ldbl_);
     PYBIND11_NUMPY_DTYPE(SimpleStructReordered, bool_, uint_, float_, ldbl_);

tests/test_numpy_dtypes.py

@@ -136,6 +136,10 @@ def test_recarray(simple_dtype, packed_dtype):
         assert_equal(arr, elements, simple_dtype)
         assert_equal(arr, elements, packed_dtype)
 
+        # Show what recarray's look like in NumPy.
+        assert type(arr[0]) == np.void
+        assert type(arr[0].item()) == tuple
+
         if dtype == simple_dtype:
             assert m.print_rec_simple(arr) == [
                 "s:0,0,0,-0",
@@ -296,6 +300,47 @@ def test_vectorize():
     np.testing.assert_array_equal(array, array_2)
 
 
+def test_cls_and_dtype_conversion(simple_dtype):
+    s = m.SimpleStruct()
+    assert s.astuple() == (False, 0, 0., 0.)
+    assert m.SimpleStruct.fromtuple(s.astuple()).astuple() == s.astuple()
+
+    s.uint_ = 2
+    assert m.f_simple(s) == 20
+
+    # Try as recarray of shape==(1,).
+    s_recarray = np.array([(False, 2, 0., 0.)], dtype=simple_dtype)
+    # Show that this will work for vectorized case.
+    np.testing.assert_array_equal(m.f_simple_vectorized(s_recarray), [20])
+
+    # Show as a scalar that inherits from np.generic.
+    s_scalar = s_recarray[0]
+    assert isinstance(s_scalar, np.void)
+    assert m.f_simple(s_scalar) == 20
+
+    # Show that an *array* scalar (np.ndarray.shape == ()) does not convert.
+    # More specifically, conversion to SimpleStruct is not implicit.
+    s_recarray_scalar = s_recarray.reshape(())
+    assert isinstance(s_recarray_scalar, np.ndarray)
+    assert s_recarray_scalar.dtype == simple_dtype
+    with pytest.raises(TypeError) as excinfo:
+        m.f_simple(s_recarray_scalar)
+    assert 'incompatible function arguments' in str(excinfo.value)
+    # Explicitly convert to m.SimpleStruct.
+    assert m.f_simple(
+        m.SimpleStruct.fromtuple(s_recarray_scalar.item())) == 20
+
+    # Show that an array of dtype=object does *not* convert.
+    s_array_object = np.array([s])
+    assert s_array_object.dtype == object
+    with pytest.raises(TypeError) as excinfo:
+        m.f_simple_vectorized(s_array_object)
+    assert 'incompatible function arguments' in str(excinfo.value)
+    # Explicitly convert to `np.array(..., dtype=simple_dtype)`
+    s_array = np.array([s.astuple()], dtype=simple_dtype)
+    np.testing.assert_array_equal(m.f_simple_vectorized(s_array), [20])
+
+
 def test_register_dtype():
     with pytest.raises(RuntimeError) as excinfo:
         m.register_dtype()