[Python] Raise minimum required Python version from 3.8 to 3.9

Python 3.8 has been end-of-life for one year already. The last platform
that used it was AlmaLinux 8, but also there it has reached end of life.
Instead, RHEL has committed to support Python 3.12 until the end-of-life
of RHEL 8 itself:
https://access.redhat.com/support/policy/updates/rhel-app-streams-life-cycle

Therefore, our CI images for `alma8` also use Python 3.12 now.

And although Python 3.9 has also reached end-of-life now, we still need
to support it because it's the system Python version on macOS.

See:
https://devguide.python.org/versions/

Author: guitargeek

.github/workflows/python_wheel_build.yml

@@ -26,7 +26,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        target: [cp38-manylinux_x86_64, cp39-manylinux_x86_64, cp310-manylinux_x86_64, cp311-manylinux_x86_64, cp312-manylinux_x86_64, cp313-manylinux_x86_64]
+        target: [cp39-manylinux_x86_64, cp310-manylinux_x86_64, cp311-manylinux_x86_64, cp312-manylinux_x86_64, cp313-manylinux_x86_64]
     name: ${{ matrix.target }}
     steps:
       - uses: actions/checkout@v4

bindings/distrdf/CMakeLists.txt

@@ -47,8 +47,6 @@ endforeach()
 add_custom_target(DistRDF ALL DEPENDS ${py_sources_in_localruntimedir})
 
 # Compile .py files
-# We include DistRDF in the build only if Python 3.8+ is used,
-# so we can directly use the main Python executable to compile the sources
 foreach(py_source ${py_sources})
   install(CODE "execute_process(COMMAND ${Python3_EXECUTABLE} -m py_compile ${localruntimedir}/${py_source})")
   install(CODE "execute_process(COMMAND ${Python3_EXECUTABLE} -O -m py_compile ${localruntimedir}/${py_source})")

bindings/pyroot/cppyy/CPyCppyy/CMakeLists.txt

@@ -94,14 +94,6 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clang"
   target_compile_options(CPyCppyy PRIVATE -Wno-cast-function-type)
 endif()
 
-# Disables warnings in Python 3.8 caused by the temporary extra filed for tp_print compatibility
-# (see https://github.com/python/cpython/blob/3.8/Include/cpython/object.h#L260).
-# Note that Python 3.8 is the lowers Python version that is still supported by
-# ROOT, so this compile option can be completely removed soon.
-if(NOT MSVC AND Python3_VERSION VERSION_LESS 3.9)
-  target_compile_options(CPyCppyy PRIVATE -Wno-missing-field-initializers)
-endif()
-
 target_compile_definitions(CPyCppyy PRIVATE NO_CPPYY_LEGACY_NAMESPACE)
 
 target_include_directories(CPyCppyy SYSTEM PUBLIC ${Python3_INCLUDE_DIRS})

cmake/modules/SearchInstalledSoftware.cmake

@@ -708,7 +708,7 @@ endif()
 if(tmva-pymva)
   list(APPEND python_components NumPy)
 endif()
-find_package(Python3 3.8 COMPONENTS ${python_components})
+find_package(Python3 3.9 COMPONENTS ${python_components})
 
 #---Check for OpenGL installation-------------------------------------------------------
 # OpenGL is required by various graf3d features that are enabled with opengl=ON,

test/PostInstall/CMakeLists.txt

@@ -19,7 +19,7 @@ if(BUILD_TESTING)
   set_tests_properties(run-hsimple   PROPERTIES FIXTURES_SETUP    HSIMPLE)
   set_tests_properties(read-hsimple  PROPERTIES FIXTURES_REQUIRED HSIMPLE)
 
-  find_package(Python3 3.8 REQUIRED)
+  find_package(Python3 3.9 REQUIRED)
   # Need to duplicate the import ROOT test because the PASS_REGULAR_EXPRESSION
   # property will disable checking the exit code of the test so import ROOT
   # might fail but ctest would not report it