This works:
import klayout.db
import klayout.lib
print(klayout.db.Library.library_names()) # says ["Basic"]
Also works:
from klayout import *
Does not work:
# import klayout.lib needs to be done before the libraries
# are used initially
import klayout.db
print(klayout.db.Library.library_names()) # says []
import klayout.lib
print(klayout.db.Library.library_names()) # says []