Forward-declare PyObject not to have to include Python.h (#910)

* Forward-declare PyObject not to have to include Python.h

* Remove unnecessary target_include_directories for python

---------

Co-authored-by: Juan Miguel Carceller <[email protected]>

Author: jmcarcell

include/podio/detail/Pythonizations.h

@@ -2,9 +2,10 @@
 #define PODIO_DETAIL_PYTHONIZATIONS_H
 
 #define PY_SSIZE_T_CLEAN
-#include <Python.h>
 #include <string>
 
+typedef struct _object PyObject;
+
 namespace podio::detail::pythonizations {
 
 // Callback function for the subscript pythonization
@@ -16,4 +17,4 @@ void pythonize_subscript(PyObject* klass, const std::string& name);
 
 } // namespace podio::detail::pythonizations
 
-#endif // PODIO_DETAIL_PYTHONIZATIONS_H
+#endif // PODIO_DETAIL_PYTHONIZATIONS_H

src/CMakeLists.txt

@@ -27,9 +27,6 @@ FUNCTION(PODIO_ADD_LIB_AND_DICT libname headers sources selection )
     $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
     $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
   )
-  target_include_directories(${libname} SYSTEM PUBLIC
-    ${Python3_INCLUDE_DIRS}
-  )
 
   # dictionary
   set(dictname ${libname}Dict)

src/Pythonizations.cc

@@ -3,6 +3,8 @@
 #include <cstring>
 #include <stdexcept>
 
+#include <Python.h>
+
 namespace podio::detail::pythonizations {
 
 // Callback function for the subscript pythonization
@@ -52,4 +54,4 @@ void pythonize_subscript(PyObject* klass, const std::string& name) {
   Py_DECREF(method);
 }
 
-} // namespace podio::detail::pythonizations
+} // namespace podio::detail::pythonizations