allow conversion to dlpack (#1120)

Author: awni

python/src/array.cpp

@@ -669,19 +669,14 @@ void init_array(nb::module_& m) {
             return a.shape(0);
           })
       .def("__iter__", [](const array& a) { return ArrayPythonIterator(a); })
-      .def(
-          "__getstate__",
-          [](const array& a) {
-            if (a.dtype() == bfloat16) {
-            }
-            return mlx_to_np_array(a);
-          })
+      .def("__getstate__", &mlx_to_np_array)
       .def(
           "__setstate__",
           [](array& arr,
              const nb::ndarray<nb::ro, nb::c_contig, nb::device::cpu>& state) {
             new (&arr) array(nd_array_to_mlx(state, std::nullopt));
           })
+      .def("__dlpack__", [](const array& a) { return mlx_to_dlpack(a); })
       .def("__copy__", [](const array& self) { return array(self); })
       .def(
           "__deepcopy__",

python/src/convert.cpp

@@ -100,8 +100,8 @@ array nd_array_to_mlx(
   }
 }
 
-template <typename Lib, typename T>
-nb::ndarray<Lib> mlx_to_nd_array(
+template <typename T, typename... NDParams>
+nb::ndarray<NDParams...> mlx_to_nd_array_impl(
     array a,
     std::optional<nb::dlpack::dtype> t = {}) {
   {
@@ -110,47 +110,51 @@ nb::ndarray<Lib> mlx_to_nd_array(
   }
   std::vector<size_t> shape(a.shape().begin(), a.shape().end());
   std::vector<int64_t> strides(a.strides().begin(), a.strides().end());
-  return nb::ndarray<Lib>(
+  return nb::ndarray<NDParams...>(
       a.data<T>(),
       a.ndim(),
       shape.data(),
-      nb::handle(),
+      nb::none(),
       strides.data(),
       t.value_or(nb::dtype<T>()));
 }
 
-template <typename Lib>
-nb::ndarray<Lib> mlx_to_nd_array(const array& a) {
+template <typename... NDParams>
+nb::ndarray<NDParams...> mlx_to_nd_array(const array& a) {
   switch (a.dtype()) {
     case bool_:
-      return mlx_to_nd_array<Lib, bool>(a);
+      return mlx_to_nd_array_impl<bool, NDParams...>(a);
     case uint8:
-      return mlx_to_nd_array<Lib, uint8_t>(a);
+      return mlx_to_nd_array_impl<uint8_t, NDParams...>(a);
     case uint16:
-      return mlx_to_nd_array<Lib, uint16_t>(a);
+      return mlx_to_nd_array_impl<uint16_t, NDParams...>(a);
     case uint32:
-      return mlx_to_nd_array<Lib, uint32_t>(a);
+      return mlx_to_nd_array_impl<uint32_t, NDParams...>(a);
     case uint64:
-      return mlx_to_nd_array<Lib, uint64_t>(a);
+      return mlx_to_nd_array_impl<uint64_t, NDParams...>(a);
     case int8:
-      return mlx_to_nd_array<Lib, int8_t>(a);
+      return mlx_to_nd_array_impl<int8_t, NDParams...>(a);
     case int16:
-      return mlx_to_nd_array<Lib, int16_t>(a);
+      return mlx_to_nd_array_impl<int16_t, NDParams...>(a);
     case int32:
-      return mlx_to_nd_array<Lib, int32_t>(a);
+      return mlx_to_nd_array_impl<int32_t, NDParams...>(a);
     case int64:
-      return mlx_to_nd_array<Lib, int64_t>(a);
+      return mlx_to_nd_array_impl<int64_t, NDParams...>(a);
     case float16:
-      return mlx_to_nd_array<Lib, float16_t>(a);
+      return mlx_to_nd_array_impl<float16_t, NDParams...>(a);
     case bfloat16:
-      return mlx_to_nd_array<Lib, bfloat16_t>(a, nb::bfloat16);
+      return mlx_to_nd_array_impl<bfloat16_t, NDParams...>(a, nb::bfloat16);
     case float32:
-      return mlx_to_nd_array<Lib, float>(a);
+      return mlx_to_nd_array_impl<float, NDParams...>(a);
     case complex64:
-      return mlx_to_nd_array<Lib, std::complex<float>>(a);
+      return mlx_to_nd_array_impl<std::complex<float>, NDParams...>(a);
   }
 }
 
 nb::ndarray<nb::numpy> mlx_to_np_array(const array& a) {
   return mlx_to_nd_array<nb::numpy>(a);
 }
+
+nb::ndarray<> mlx_to_dlpack(const array& a) {
+  return mlx_to_nd_array<>(a);
+}

python/src/convert.h

@@ -13,4 +13,6 @@ using namespace mlx::core;
 array nd_array_to_mlx(
     nb::ndarray<nb::ro, nb::c_contig, nb::device::cpu> nd_array,
     std::optional<Dtype> dtype);
+
 nb::ndarray<nb::numpy> mlx_to_np_array(const array& a);
+nb::ndarray<> mlx_to_dlpack(const array& a);

python/tests/test_array.py

@@ -1722,6 +1722,20 @@ def test_add_numpy(self):
         self.assertEqual(z.dtype, mx.int32)
         self.assertEqual(z.item(), 3)
 
+    def test_dlpack(self):
+        x = mx.array(1, dtype=mx.int32)
+        y = np.from_dlpack(x)
+        self.assertTrue(mx.array_equal(y, x))
+
+        x = mx.array([[1.0, 2.0], [3.0, 4.0]])
+        y = np.from_dlpack(x)
+        self.assertTrue(mx.array_equal(y, x))
+
+        x = mx.arange(16).reshape(4, 4)
+        x = x[::2, ::2]
+        y = np.from_dlpack(x)
+        self.assertTrue(mx.array_equal(y, x))
+
 
 if __name__ == "__main__":
     unittest.main()