array: implement array resize

include/pybind11/numpy.h

@@ -129,6 +129,11 @@ struct npy_api {
         NPY_STRING_, NPY_UNICODE_, NPY_VOID_
     };
 
+    typedef struct {
+        Py_intptr_t *ptr;
+        int len;
+    } PyArray_Dims;
+
     static npy_api& get() {
         static npy_api api = lookup();
         return api;
@@ -159,6 +164,7 @@ struct npy_api {
                                              Py_ssize_t *, PyObject **, PyObject *);
     PyObject *(*PyArray_Squeeze_)(PyObject *);
     int (*PyArray_SetBaseObject_)(PyObject *, PyObject *);
+    PyObject* (*PyArray_Resize_)(PyObject*, PyArray_Dims*, int, int);
 private:
     enum functions {
         API_PyArray_GetNDArrayCFeatureVersion = 211,
@@ -168,6 +174,7 @@ private:
         API_PyArray_DescrFromType = 45,
         API_PyArray_DescrFromScalar = 57,
         API_PyArray_FromAny = 69,
+        API_PyArray_Resize = 80,
         API_PyArray_NewCopy = 85,
         API_PyArray_NewFromDescr = 94,
         API_PyArray_DescrNewFromType = 9,
@@ -197,6 +204,7 @@ private:
         DECL_NPY_API(PyArray_DescrFromType);
         DECL_NPY_API(PyArray_DescrFromScalar);
         DECL_NPY_API(PyArray_FromAny);
+        DECL_NPY_API(PyArray_Resize);
         DECL_NPY_API(PyArray_NewCopy);
         DECL_NPY_API(PyArray_NewFromDescr);
         DECL_NPY_API(PyArray_DescrNewFromType);
@@ -652,6 +660,21 @@ public:
         return reinterpret_steal<array>(api.PyArray_Squeeze_(m_ptr));
     }
 
+    /// Resize array to given shape
+    /// If refcheck is true and more that one reference exist to this array
+    /// then resize will succeed only if it makes a reshape, i.e. original size doesn't change
+    void resize(ShapeContainer new_shape, bool refcheck = true) {
+        detail::npy_api::PyArray_Dims d = {
+            new_shape->data(), int(new_shape->size())
+        };
+        // try to resize, set ordering param to -1 cause it's not used anyway
+        object new_array = reinterpret_steal<object>(
+            detail::npy_api::get().PyArray_Resize_(m_ptr, &d, int(refcheck), -1)
+        );
+        if (!new_array) throw error_already_set();
+        if (isinstance<array>(new_array)) { *this = std::move(new_array); }
+    }
+
     /// Ensure that the argument is a NumPy array
     /// In case of an error, nullptr is returned and the Python error is cleared.
     static array ensure(handle h, int ExtraFlags = 0) {

tests/test_numpy_array.cpp

@@ -273,4 +273,25 @@ test_initializer numpy_array([](py::module &m) {
     sm.def("array_initializer_list", []() { return py::array_t<float>({ 1, 2 }); });
     sm.def("array_initializer_list", []() { return py::array_t<float>({ 1, 2, 3 }); });
     sm.def("array_initializer_list", []() { return py::array_t<float>({ 1, 2, 3, 4 }); });
-});
+
+    // reshape array to 2D without changing size
+    sm.def("array_reshape2", [](py::array_t<double> a) {
+        const size_t dim_sz = (size_t)std::sqrt(a.size());
+        if (dim_sz * dim_sz != a.size())
+            throw std::domain_error("array_reshape2: input array total size is not a squared integer");
+        a.resize({dim_sz, dim_sz});
+    });
+
+    // resize to 3D array with each dimension = N
+    sm.def("array_resize3", [](py::array_t<double> a, size_t N, bool refcheck) {
+        a.resize({N, N, N}, refcheck);
+    });
+
+    // return 2D array with Nrows = Ncols = N
+    sm.def("create_and_resize", [](size_t N) {
+        py::array_t<double> a;
+        a.resize({N, N});
+        std::fill(a.mutable_data(), a.mutable_data() + a.size(), 42.);
+        return a;
+    });
+});
\ No newline at end of file

tests/test_numpy_array.py

@@ -389,3 +389,38 @@ def test_array_failure():
     with pytest.raises(ValueError) as excinfo:
         array_t_fail_test()
     assert str(excinfo.value) == 'cannot create a pybind11::array_t from a nullptr'
+
+
+def test_array_resize(msg):
+    from pybind11_tests.array import (array_reshape2, array_resize3)
+
+    a = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9], dtype='float64')
+    array_reshape2(a)
+    assert(a.size == 9)
+    assert(np.all(a == [[1, 2, 3], [4, 5, 6], [7, 8, 9]]))
+
+    # total size change should succced with refcheck off
+    array_resize3(a, 4, False)
+    assert(a.size == 64)
+    # ... and fail with refcheck on
+    try:
+        array_resize3(a, 3, True)
+    except ValueError as e:
+        assert(str(e).startswith("cannot resize an array"))
+    # transposed array doesn't own data
+    b = a.transpose()
+    try:
+        array_resize3(b, 3, False)
+    except ValueError as e:
+        assert(str(e).startswith("cannot resize this array: it does not own its data"))
+    # ... but reshape should be fine
+    array_reshape2(b)
+    assert(b.shape == (8, 8))
+
+
+@pytest.unsupported_on_pypy
+def test_array_create_and_resize(msg):
+    from pybind11_tests.array import create_and_resize
+    a = create_and_resize(2)
+    assert(a.size == 4)
+    assert(np.all(a == 42.))