This patch follows the first mechanism listed by Martin. The change in configure.ac fixes the problem described by Victor, it does not generate an empty Objects/typeslots.inc file when python is not found that would cause the cryptic " <class 'RuntimeError'>: invalid slot offset" errors on subsequent builds.

The change in Objects/typeslots.py is not strictly necessary to fix the problem but prevents typeslots.py to create an invalid typeslots.inc file through the previous stdout redirection mechanism when, for example, typeslots.py is modified inadvertently with a change that is not python2 compatible and typeslots.py is run by python2 and fails.