It's a good idea to keep your valuables tucked out of sight when you're traveling in Paris, and it can be difficult to do that with a purse. There are stories about pickpockets who will cut through the side of your bag to locate your wallet or other precious objects, and for that reason, I like to keep my hands and arms free when I'm wandering through Paris.
I bought this jacket a few months before leaving Los Angeles, and it was perfect for riding around on the Paris metro. I love the fact that there are so many pockets, and since the pockets have buttons on them, it's nearly impossible for someone to slip their hand inside and steal my wallet. It's actually a man's jacket (go figure, so much more practical than a woman's jacket), but it looks great over pants or a dress.