I won't get into details. But according to laws in my country you can carry a knife legally if you have no intention of using it to cause bodily harm or use it as a weapon, spring assisted knives, and anything with knuckles or any double edged blades are illegal to carry. And if you do happen to carry a knife - if there's justified reason for it - it's good. But it's harder to justify carrying a large knife. And if you say "self defense" - they will question you what kind of places do you visit so you need that? What job you do? Do let's say you're coming home from work and group of "ultras" who just watched football start to harrass you which club did you root for or to recite their anthem... you have no idea about anything since you don't watch football so you tell them to f*ck off. Then bigger guy gets physically agressive and you stab him several times with a screwdriver. And other 3 guys run away in fear... So later, you see your screwdriver handed to the judge and lawyer of the asshole you stabbed asks the judge "What kind of people walk around with this? Is there any need for it? What was the intent of young man carrying such an object?". So, the idiot who tried to beat you up is playing the victim. But you realize that it's rather dumb question from them, and you just say how it is: "I'm electician. I work at construction site, I was going home from work when he attacked me with his drunken friends". And your defense hands them the same thing that was written in police report and also checked. It's logical that electrician will have a screwdriver. Then, they try to claim that you provoked the group of drunken idiots, but lucky for you - judge isn't having any of it. And you walk out as a free man.