I traveled to France a decade ago with my Bike Friday Pocket Rocket. I share your desire not to lug around heavy locks.

I managed without any sort of lock. It was just me, so I didn't have anyone else to watch my bike. If a shopkeeper allowed, I'd fold my bike and take it inside. If not, I'd take the front wheel off, fold it, leave the rest just outside the door, and take the wheel with me. Much harder to ride away with a bike if it only has one wheel, though that certainly doesn't make it theft proof. Sometimes I'd velcro strap or bungee the rest of the bike together so it became a bit of a mess to untangle, much less unfold.

I was surprised how much resistance some shopkeepers had to a folding bike. Yes, I understand Europe has tighter quarters, but the whole idea of a folding bike is to take it with you everywhere. Not all shopkeepers allow this. I learned to frequent the ones that did. Less of an issue in the outskirts, away from major cities. It seemed the closer I got to Paris, the less accommodating the shopkeepers were.

Hope you have a wonderful time. I spent my week riding, touring museums and doing street photography. It was a blast.