Do not enforce 3.9 yet

Author: ax3l

cmake/dependencies/pybind11.cmake

@@ -83,9 +83,9 @@ set(openPMD_pybind11_branch "v2.13.6"
     "Repository branch for openPMD_pybind11_repo if(openPMD_USE_INTERNAL_PYBIND11)")
 
 if(openPMD_USE_PYTHON STREQUAL AUTO)
-    find_package(Python 3.9.0 COMPONENTS Interpreter Development.Module)
+    find_package(Python 3.8.0 COMPONENTS Interpreter Development.Module)
 elseif(openPMD_USE_PYTHON)
-    find_package(Python 3.9.0 COMPONENTS Interpreter Development.Module REQUIRED)
+    find_package(Python 3.8.0 COMPONENTS Interpreter Development.Module REQUIRED)
 else()
     set(openPMD_HAVE_PYTHON FALSE)
 endif()

setup.py

@@ -203,7 +203,7 @@ def build_extension(self, ext):
     cmdclass=dict(build_ext=CMakeBuild),
     # scripts=['openpmd-ls'],
     zip_safe=False,
-    python_requires='>=3.9',
+    python_requires='>=3.8',  # left for Ubuntu 20.04, truly ">=3.9"
     # tests_require=['pytest'],
     install_requires=install_requires,
     # see: src/bindings/python/cli