To leave the airport in Paris, you have to pass through the passport checkpoint.
Because you are a South African citizen, you need a visa. The duration of your intended stay is not relevant to the visa requirement (as long as your stay doesn't exceed 90 days). Neither is the fact that you have a US visa.
(Some people need an airport transit visa if they don't plan to pass through passport control, but South African citizens are not subjected to that requirement.)
Do I need a visa for a short layover in Paris?
To leave the airport, yes, you do. To stay in the airport, no, you don't.