backporting importlib.metadata for python<3.8

setup.py

@@ -974,6 +974,9 @@ if __name__ == "__main__":
         package_data={config.root: ["src/pymod/distutils_src/klayout/*.pyi"]},
         data_files=[(config.root, ["src/pymod/distutils_src/klayout/py.typed"])],
         include_package_data=True,
+        install_requires = [
+            'importlib-metadata >= 1.0 ; python_version < "3.8"',
+        ],
         ext_modules=[_tl, _gsi, _pya, _rba, _db, _lib, _rdb, _lym, _laybasic, _layview, _ant, _edt, _img]
             + db_plugins
             + [tl, db, lib, rdb, lay],

src/pymod/distutils_src/klayout/__init__.py

@@ -1,5 +1,8 @@
-
-from importlib import metadata
+import sys
+if sys.version_info >= (3, 8):
+    from importlib import metadata
+else:
+    import importlib_metadata as metadata
 
 try:
     __version__ = metadata.version('klayout')