Move Background dtor to public, use shared_ptr for pybind11

include/lsst/afw/math/Background.h

@@ -257,14 +257,14 @@ class Background {
      * is mostly used to implement persistence.
      */
     explicit Background(lsst::geom::Box2I const imageBBox, int const nx, int const ny);
-    /// dtor
-    virtual ~Background() = default;
 
 public:
     typedef float InternalPixelT;  ///< type used for any internal images, and returned by getApproximate
 
     Background(Background const&) = delete;
     Background(Background&&) = delete;
+    /// dtor
+    virtual ~Background() = default;
     Background& operator=(Background const&) = delete;
     Background& operator=(Background&&) = delete;
 

python/lsst/afw/math/background/background.cc

@@ -133,13 +133,7 @@ PYBIND11_MODULE(background, mod) {
                              (std::shared_ptr<ApproximateControl> (BackgroundControl::*)()) &
                                      BackgroundControl::getApproximateControl);
 
-    /* Note that, in this case, the holder type must be unique_ptr to enable usage
-     * of py::nodelete, which in turn is needed because Background has a protected
-     * destructor. Adding py::nodelete prevents pybind11 from calling the destructor
-     * when the pointer is destroyed. Thus care needs to be taken to prevent leaks.
-     * Basically Background should only ever be used as a base class (without data
-     * members). */
-    py::class_<Background, std::unique_ptr<Background, py::nodelete>> clsBackground(mod, "Background");
+    py::class_<Background, std::shared_ptr<Background>> clsBackground(mod, "Background");
 
     /* Members */
     declareGetImage<float>(clsBackground, "F");
@@ -179,4 +173,4 @@ PYBIND11_MODULE(background, mod) {
 }
 }
 }
-}  // lsst::afw::math
+}  // lsst::afw::math