add __cuda_array_interface__ and tests

- fixes #4

.github/workflows/test.yml

@@ -52,6 +52,13 @@ jobs:
     - name: Run setup-python
       run: setup-python -p${{ matrix.python }}
     - run: pip install -U -e .[dev]
+    - name: pip install cupy
+      run: |
+        CUVER=$(ls /usr/local/cuda-* -d | sed -r 's/\/usr\/local\/cuda-([0-9]+)\.([0-9]+)/\1\2/' | sort -nr | head -n1)
+        echo CUDA Tookit: $CUVER
+        [[ $CUVER -gt 111 ]] && CUVER=111
+        echo Installing: cupy-cuda$CUVER
+        pip install cupy-cuda$CUVER
     - run: pytest
     - run: codecov
     - name: Post Run setup-python

cuvec/helpers.py

@@ -49,6 +49,12 @@ def __new__(cls, arr):
             (do not do `cuvec.CuVec((42, 1337))`;
             instead use `cuvec.zeros((42, 137))`"""))
 
+    @property
+    def __cuda_array_interface__(self):
+        res = self.__array_interface__
+        return {
+            'shape': res['shape'], 'typestr': res['typestr'], 'data': res['data'], 'version': 3}
+
 
 def zeros(shape, dtype="float32"):
     """

tests/test_helpers.py

@@ -1,7 +1,7 @@
 import logging
 
 import numpy as np
-from pytest import mark, raises
+from pytest import importorskip, mark, raises
 
 import cuvec as cu
 
@@ -81,3 +81,15 @@ def test_asarray():
     assert s.cuvec != v.cuvec
     assert (s == v[1:]).all()
     assert np.asarray(s.cuvec).data != np.asarray(v.cuvec).data
+
+
+def test_cuda_array_interface():
+    cupy = importorskip("cupy")
+    v = cu.asarray(np.random.random(shape))
+    c = cupy.asarray(v)
+
+    assert (c == v).all()
+    c[0, 0, 0] = 1
+    assert c[0, 0, 0] == v[0, 0, 0]
+    c[0, 0, 0] = 0
+    assert c[0, 0, 0] == v[0, 0, 0]