[Python] Use separate GetBuffer helper in Pythonization library

The `Utiliy::GetBuffer` function from CPyCppyy is an overkill for the
simple usecase in the ROOT Pythonization library. We can have our own
helper there, avoiding yet another usage of internal CPyCppyy functions.

Author: guitargeek

bindings/pyroot/pythonizations/src/PyROOTModule.cxx

@@ -144,6 +144,39 @@ PyObject *PyObjRefCounterAsStdAny(PyObject * /*self*/, PyObject *args)
                                          /*python_owns=*/true);
 }
 
+// Helper function to get the pointer to a buffer (heavily simplified copy of
+// CPyCppyy::Utility::GetBuffer).
+void GetBuffer(PyObject *pyobject, void *&buf)
+{
+   buf = nullptr;
+
+   // Exclude text-like objects (policy decision)
+   if (PyBytes_Check(pyobject) || PyUnicode_Check(pyobject))
+      return;
+
+   // Fast path: bytearray
+   if (PyByteArray_CheckExact(pyobject)) {
+      buf = PyByteArray_AsString(pyobject);
+      return;
+   }
+
+   // Buffer protocol
+   if (PyObject_CheckBuffer(pyobject)) {
+      // Avoid potential issues with empty sequences
+      if (PySequence_Check(pyobject) && PySequence_Size(pyobject) == 0)
+         return;
+
+      Py_buffer view;
+      if (PyObject_GetBuffer(pyobject, &view, PyBUF_SIMPLE) == 0) {
+         if (view.buf && view.len > 0)
+            buf = view.buf;
+         PyBuffer_Release(&view);
+      } else {
+         PyErr_Clear();
+      }
+   }
+}
+
 } // namespace PyROOT
 
 // Methods offered by the interface

bindings/pyroot/pythonizations/src/PythonLimitedAPI.h

@@ -1,12 +1,18 @@
 #ifndef ROOT_PythonLimitedAPI_h
 #define ROOT_PythonLimitedAPI_h
 
-// Use what is in the limited API since Python 3.10
+// Use what is in the limited API since Python 3.11 if we're building with at
+// least Python 3.11. The reason why we can't go back to 3.10 is that that at
+// that point, the new buffer interface was not part of the limited API yet.
+#if PY_VERSION_HEX >= 0x030B0000
+
 // On Windows we can't use the stable ABI yet: it requires linking against a
 // different libpython, so as long as we don't build all translation units in
 // the ROOT Pythonization library with the stable ABI we should not use it.
 #ifndef _WIN32
-#define Py_LIMITED_API 0x030A0000
+#define Py_LIMITED_API 0x030B0000
+#endif
+
 #endif
 
 #include <Python.h>

bindings/pyroot/pythonizations/src/TClassPyz.cxx

@@ -22,6 +22,10 @@
 
 using namespace CPyCppyy;
 
+namespace PyROOT{
+void GetBuffer(PyObject *pyobject, void *&buf);
+}
+
 // Cast the void* returned by TClass::DynamicCast to the right type
 PyObject *TClassDynamicCastPyz(PyObject *self, PyObject *args)
 {
@@ -50,7 +54,7 @@ PyObject *TClassDynamicCastPyz(PyObject *self, PyObject *args)
    } else if (PyInt_Check(pyobject) || PyLong_Check(pyobject)) {
       address = (void *)PyLong_AsLongLong(pyobject);
    } else {
-      Utility::GetBuffer(pyobject, '*', 1, address, false);
+      PyROOT::GetBuffer(pyobject, address);
    }
 
    // Now use binding to return a usable class. Upcast: result is a base.

bindings/pyroot/pythonizations/src/TTreePyz.cxx

@@ -13,7 +13,6 @@
 #include "../../cppyy/CPyCppyy/src/CPyCppyy.h"
 #include "../../cppyy/CPyCppyy/src/CPPInstance.h"
 #include "../../cppyy/CPyCppyy/src/ProxyWrappers.h"
-#include "../../cppyy/CPyCppyy/src/Utility.h"
 #include "../../cppyy/CPyCppyy/src/Dimensions.h"
 
 #include "CPyCppyy/API.h"
@@ -47,6 +46,10 @@ TClass *GetTClass(PyObject *pyobj)
 
 using namespace CPyCppyy;
 
+namespace PyROOT{
+void GetBuffer(PyObject *pyobject, void *&buf);
+}
+
 static TBranch *SearchForBranch(TTree *tree, const char *name)
 {
    TBranch *branch = tree->GetBranch(name);
@@ -251,7 +254,7 @@ PyObject *TryBranchLeafListOverload(int argc, PyObject *args)
       if (CPyCppyy::Instance_Check(address))
          buf = CPyCppyy::Instance_AsVoidPtr(address);
       else
-         Utility::GetBuffer(address, '*', 1, buf, false);
+         PyROOT::GetBuffer(address, buf);
 
       if (buf) {
          TBranch *branch = nullptr;
@@ -331,7 +334,7 @@ PyObject *TryBranchPtrToPtrOverloads(int argc, PyObject *args)
             argc += 1;
          }
       } else {
-         Utility::GetBuffer(address, '*', 1, buf, false);
+         PyROOT::GetBuffer(address, buf);
       }
 
       if (buf && !klName.empty()) {