python: Use `std::optional` to accept `None` for empty images

python/src/interface.cpp

@@ -16,6 +16,7 @@ namespace py = pybind11;
 #include <string>
 #include <cstdint>
 #include <memory>
+#include <optional>
 
 
 imfu::Type getTypeFromNumpyFormat(std::string const& fmt, int channels = 1) {
@@ -332,11 +333,13 @@ PYBIND11_MODULE(_imagefusion, module) {
 
     py::class_<imfu::Image, imfu::ConstImage> image(module, "Image", py::buffer_protocol());
     image.def(py::init());
-    image.def(py::init([](py::none /*empty*/) { return new imfu::Image(); }));
     image.def(py::init<std::string const&, std::vector<int>, imfu::Rectangle, bool, bool, bool>());
-    image.def(py::init([](py::buffer b) -> imfu::Image* { // converts from np.array to imfu::Image
+    image.def(py::init([](std::optional<py::buffer> b) -> imfu::Image* { // converts from np.array to imfu::Image
+        if (!b.has_value()) // allows Image(numpy_img), where numpy_img may be None
+            return new imfu::Image();
+
         /* Request a buffer descriptor from Python */
-        auto info = std::make_unique<py::buffer_info>(b.request());
+        auto info = std::make_unique<py::buffer_info>(b->request());
 
         if (info->ndim != 2 && info->ndim != 3)
             throw std::runtime_error("Incompatible buffer dimension: " + std::to_string(info->ndim) + "!");
@@ -393,7 +396,8 @@ PYBIND11_MODULE(_imagefusion, module) {
           }
           return img;
         }
-    }));
+    }), py::arg("b") = py::none()
+    );
 
     image.def_buffer([](imfu::Image& img) -> py::buffer_info { // converts from imfu::Image to np.array
       return py::buffer_info(