Toulouse was not the beginning of a camera-obsession with doors, but it had so many different styles and types that it certainly fertilized the passion. We visited the city in 2013 for a conference.
This is the right half of a true French door, the one which is used all the time as opposed to the more rarely opened left half. Notice the brutal lock plate. But most of all, check out the location of the door knob. It is centered in the panel, which was true of most of the older doors I saw in Switzerland and France, less true in Amsterdam, and not quite uncommon in Stockholm.
As far as I can tell, the sole reason for centering the knob is æsthetics.