pybind/pybind11
1
0
Fork 0
mirror of https://github.com/pybind/pybind11.git synced 2026-05-12 01:10:34 +00:00
Code Issues Packages Projects Releases Wiki Activity

Add the buffer interface for wrapped STL vectors

Browse Source 
Allows use of vectors as python buffers, so for example they can be adopted without a copy by numpy.asarray
Allows faster conversion of buffers to vectors by copying instead of individually casting the elements
This commit is contained in:
Patrick Stewart
2016-11-08 13:03:34 +00:00
committed by Wenzel Jakob
parent 16afbcef46
commit 5467979588
3 changed files with 130 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

46
include/pybind11/stl_bind.h
View File

@@ -326,6 +326,49 @@ template <typename Vector, typename Class_> auto vector_if_insertion_operator(Cl
);
}
// Provide the buffer interface for vectors if we have data() and we have a format for it
// GCC seems to have "void std::vector<bool>::data()" - doing SFINAE on the existence of data() is insufficient, we need to check it returns an appropriate pointer
template <typename Vector, typename = void>
struct vector_has_data_and_format : std::false_type {};
template <typename Vector>
struct vector_has_data_and_format<Vector, enable_if_t<std::is_same<decltype(py::format_descriptor<typename Vector::value_type>::format(), std::declval<Vector>().data()), typename Vector::value_type*>::value>> : std::true_type {};
// Add the buffer interface to a vector
template <typename Vector, typename Class_, typename... Args>
enable_if_t<detail::any_of<std::is_same<Args, py::buffer_protocol>...>::value>
vector_buffer(Class_& cl) {
using T = typename Vector::value_type;
static_assert(vector_has_data_and_format<Vector>::value, "There is not an appropriate format descriptor for this vector");
// numpy.h declares this for arbitrary types, but it may raise an exception and crash hard at runtime if PYBIND11_NUMPY_DTYPE hasn't been called, so check here
py::format_descriptor<T>::format();
cl.def_buffer([](Vector& v) -> py::buffer_info {
return py::buffer_info(v.data(), sizeof(T), py::format_descriptor<T>::format(), 1, {v.size()}, {sizeof(T)});
});
cl.def("__init__", [](Vector& vec, py::buffer buf) {
auto info = buf.request();
if (info.ndim != 1 || info.strides[0] <= 0 || info.strides[0] % sizeof(T))
throw pybind11::type_error("Only valid 1D buffers can be copied to a vector");
if (!detail::compare_buffer_info<T>::compare(info) || sizeof(T) != info.itemsize)
throw pybind11::type_error("Format mismatch (Python: " + info.format + " C++: " + py::format_descriptor<T>::format() + ")");
new (&vec) Vector();
vec.reserve(info.shape[0]);
T *p = static_cast<T*>(info.ptr);
auto step = info.strides[0] / sizeof(T);
T *end = p + info.shape[0] * step;
for (; p < end; p += step)
vec.push_back(*p);
});
return;
}
template <typename Vector, typename Class_, typename... Args>
enable_if_t<!detail::any_of<std::is_same<Args, py::buffer_protocol>...>::value> vector_buffer(Class_&) {}
NAMESPACE_END(detail)
//
@@ -337,6 +380,9 @@ pybind11::class_<Vector, holder_type> bind_vector(pybind11::module &m, std::stri
Class_ cl(m, name.c_str(), std::forward<Args>(args)...);
// Declare the buffer interface if a py::buffer_protocol() is passed in
detail::vector_buffer<Vector, Class_, Args...>(cl);
cl.def(pybind11::init<>());
// Register copy constructor (if possible)