Make pythonization for collection subscript header only again

include/podio/detail/Pythonizations.h

@@ -1,18 +1,62 @@
 #ifndef PODIO_DETAIL_PYTHONIZATIONS_H
 #define PODIO_DETAIL_PYTHONIZATIONS_H
 
-#include <string>
+// NOTE: Python.h must be included before any standard headers and should be preceded by PY_SSIZE_T_CLEAN definition
+#define PY_SSIZE_T_CLEAN
+#include <Python.h>
 
-typedef struct _object PyObject;
+#include <cstring>
+#include <stdexcept>
+#include <string>
 
 namespace podio::detail::pythonizations {
 
 // Callback function for the subscript pythonization
 // Calls the `at` method and change exception type to IndexError if the index is out of range
-PyObject* subscript(PyObject* self, PyObject* index);
+inline PyObject* subscript(PyObject* self, PyObject* index) {
+  PyObject* result = PyObject_CallMethod(self, "at", "O", index);
+  if (!result) {
+    PyObject* exc = PyErr_Occurred();
+    // Check if the exception is `cppyy.gbl.std.out_of_range`
+    // Since PyImport_ImportModule("cppyy") fails, this workaround checks the exception name
+    if (exc && PyObject_HasAttrString(exc, "__name__")) {
+      PyObject* exc_name = PyObject_GetAttrString(exc, "__name__");
+      if (exc_name) {
+        const char* name_cstr = PyUnicode_AsUTF8(exc_name);
+        if (name_cstr && strcmp(name_cstr, "out_of_range") == 0) {
+          PyErr_Clear();
+          PyErr_SetString(PyExc_IndexError, "Index out of range");
+        }
+        Py_DECREF(exc_name);
+      }
+    }
+  }
+  return result;
+}
 
 // Helper to register the subscript pythonization callback as `__getitem__` method
-void pythonize_subscript(PyObject* klass, const std::string& name);
+inline void pythonize_subscript(PyObject* klass, const std::string& name) {
+  static PyMethodDef ml = {"subscript_pythonization", subscript, METH_VARARGS, R"(
+        Raise an `IndexError` exception if an index is invalid.
+        The `__getitem__` will return immutable datatype objects instead of the mutable ones.
+  )"};
+  auto* func = PyCFunction_New(&ml, klass);
+  if (!func) {
+    throw std::runtime_error("Failed to create Python subscript function for class " + name);
+  }
+  auto* method = PyInstanceMethod_New(func);
+  if (!method) {
+    Py_DECREF(func);
+    throw std::runtime_error("Failed to create Python instance method for subscript for class " + name);
+  }
+  if (0 != PyObject_SetAttrString(klass, "__getitem__", method)) {
+    Py_DECREF(method);
+    Py_DECREF(func);
+    throw std::runtime_error("Failed to set __getitem__ attribute on class " + name);
+  }
+  Py_DECREF(func);
+  Py_DECREF(method);
+}
 
 } // namespace podio::detail::pythonizations
 

src/CMakeLists.txt

@@ -58,7 +58,6 @@ SET(core_sources
   MurmurHash3.cpp
   SchemaEvolution.cc
   Glob.cc
-  Pythonizations.cc
   )
 
 SET(core_headers
@@ -77,7 +76,7 @@ SET(core_headers
 
 PODIO_ADD_LIB_AND_DICT(podio "${core_headers}" "${core_sources}" selection.xml)
 target_compile_options(podio PRIVATE -pthread)
-target_link_libraries(podio PRIVATE Python3::Python)
+target_link_libraries(podio PUBLIC Python3::Module)
 # For Frame.h
 if (ROOT_VERSION VERSION_LESS 6.36)
   target_compile_definitions(podio PUBLIC PODIO_ROOT_OLDER_6_36=1)