Ben Zumeta wrote: the statistics on guns, their relationship to the owner's safety, and who actually falls victim to their use (the owner, and those closest to them are far more likely to be harmed by them than any criminal), might give caution to those who consider their usefulness for protection.
I would feel the same way about the other suggestion of "a pocket knife". Unless you are experienced in the wielding of one, carrying a knife is probably the best way to get even more hurt yourself than the person you are trying to defend yourself from. With any knife, you have to get real close to the other person to have any effect with it, and then they'll have it straight off you as they probably come into contact with knives far more than you do. Just waving it from a distance is only likely to rile them, make them laugh or encourage them to come in and get it off you. This is what I have told my son who I found sleeping with a knife under his pillow because it "made him feel safer".
Myself, I favour a 30" blackthorn stick which I am very experienced at waving around at close quarters and NOT hitting people with, so I reckon if I ever wanted to actually make contact my spatial awareness of it would be acute enough I could make it felt. At the very least I could poke the antagonist and keep them away from me.
Or the pepper spray.