len() and pedestal subtraction (#328)

Collection of small improvements in usability: 

- NDView works for large arrays
- Direct subtraction of Pedestal from np.array
- len() support for python bindings of files

python/src/bind_RawFile.hpp

@@ -280,6 +280,7 @@ void define_raw_file_io_bindings(py::module &m) {
         .def("tell", &RawFile::tell, R"(
             Return the current frame number.)")
         .def_property_readonly("total_frames", &RawFile::total_frames)
+        .def("__len__", &RawFile::total_frames)
         .def("rows", static_cast<size_t (RawFile::*)() const>(&RawFile::rows))
         .def(
             "rows",

python/src/ctb_raw_file.hpp

@@ -226,5 +226,7 @@ void define_ctb_raw_file_io_bindings(py::module &m) {
         .def_property_readonly("image_size_in_bytes",
                                &CtbRawFile::image_size_in_bytes)
 
-        .def_property_readonly("frames_in_file", &CtbRawFile::frames_in_file);
+        .def_property_readonly("frames_in_file", &CtbRawFile::frames_in_file)
+        .def_property_readonly("total_frames", &CtbRawFile::total_frames)
+        .def("__len__", &CtbRawFile::total_frames);
 }

python/src/file.hpp

@@ -60,6 +60,7 @@ void define_file_io_bindings(py::module &m) {
         .def("seek", &File::seek)
         .def("tell", &File::tell)
         .def_property_readonly("total_frames", &File::total_frames)
+        .def("__len__", &File::total_frames)
         .def_property_readonly("rows", &File::rows)
         .def_property_readonly("cols", &File::cols)
         .def_property_readonly("bitdepth", &File::bitdepth)

python/src/jungfrau_data_file.hpp

@@ -72,6 +72,7 @@ void define_jungfrau_data_file_io_bindings(py::module &m) {
         .def_property_readonly("bitdepth", &JungfrauDataFile::bitdepth)
         .def_property_readonly("current_file", &JungfrauDataFile::current_file)
         .def_property_readonly("total_frames", &JungfrauDataFile::total_frames)
+        .def("__len__", &JungfrauDataFile::total_frames)
         .def_property_readonly("n_files", &JungfrauDataFile::n_files)
         .def("read_frame", &read_dat_frame,
              R"(

python/src/pedestal.hpp

@@ -5,6 +5,7 @@
 
 #include <cstdint>
 #include <filesystem>
+#include <pybind11/numpy.h>
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
 
@@ -12,7 +13,8 @@ namespace py = pybind11;
 
 template <typename SUM_TYPE>
 void define_pedestal_bindings(py::module &m, const std::string &name) {
-    py::class_<Pedestal<SUM_TYPE>>(m, name.c_str())
+
+    py::class_<Pedestal<SUM_TYPE>>(m, name.c_str(), py::buffer_protocol())
         .def(py::init<int, int, int>())
         .def(py::init<int, int>())
         .def("mean",
@@ -50,6 +52,23 @@ void define_pedestal_bindings(py::module &m, const std::string &name) {
                  *std = self.std();
                  return return_image_data(std);
              })
+        .def(
+            "__array_ufunc__",
+            [](py::object self, py::object ufunc, const std::string &method,
+               py::args inputs, py::kwargs kwargs) -> py::object {
+                if (method != "__call__" || inputs.size() != 2 ||
+                    inputs[1].ptr() != self.ptr() ||
+                    py::cast<std::string>(ufunc.attr("__name__")) !=
+                        "subtract") {
+                    return py::reinterpret_borrow<py::object>(
+                        Py_NotImplemented);
+                }
+
+                auto mean =
+                    py::module_::import("builtins").attr("memoryview")(self);
+                return ufunc(inputs[0], mean, **kwargs);
+            },
+            "Support subtracting a Pedestal from a NumPy array.")
         .def("clear", py::overload_cast<>(&Pedestal<SUM_TYPE>::clear))
         .def_property_readonly("rows", &Pedestal<SUM_TYPE>::rows)
         .def_property_readonly("cols", &Pedestal<SUM_TYPE>::cols)
@@ -84,5 +103,17 @@ void define_pedestal_bindings(py::module &m, const std::string &name) {
                 pedestal.push_no_update(v);
             },
             py::arg().noconvert())
-        .def("update_mean", &Pedestal<SUM_TYPE>::update_mean);
-}
+        .def("update_mean", &Pedestal<SUM_TYPE>::update_mean)
+        .def_buffer([](Pedestal<SUM_TYPE> &self) {
+            auto mean = self.view();
+            return py::buffer_info(
+                const_cast<SUM_TYPE *>(mean.data()), sizeof(SUM_TYPE),
+                py::format_descriptor<SUM_TYPE>::format(), 2,
+                {static_cast<py::ssize_t>(mean.shape(0)),
+                 static_cast<py::ssize_t>(mean.shape(1))},
+                {static_cast<py::ssize_t>(mean.strides()[0] * sizeof(SUM_TYPE)),
+                 static_cast<py::ssize_t>(mean.strides()[1] *
+                                          sizeof(SUM_TYPE))},
+                true);
+        });
+}