Upvote:1
You have to use your Portuguese passport at the French and Portuguese border, as you'll enter Schengen - a single country for border purposes - in Paris, and exit in Lisbon.
Thus, the Portuguese passport is also the one to present at check-in.
It has to be valid on the day you enter France (and Portugal on the way back) in order for check-in staff in South Africa/Cape Verde to let you board.
Otherwise, you have to renew your Portuguese passport or get a Portuguese ID card.