Here is a reference guide to Los Angeles knife law. People can review these laws online at their own lesiure-
Los Angeles Municipal Codes-
Section 55.10 refers to knife carry.
55.10 a. defines what the municipality of LA considers to be a "knife".
55.10 b. explains the prohibitions on knife carry in the municipality of LA.
55.10 c. explains the exemptions to the prohibitions in 55.10 b.
Los Angeles County Penal Code-
13.62.010 defines what the county of LA considers to be a "knife".
13.62.020 explains the prohibitions of knife carry in the county of LA.
13.62.030 explains the exemptions to the prohibitions in 13.62.020.
13.62.040 explains the penalties for violating the prohibitions in 13.62.020.
The LA municipal code and the LA county code are virtually identical with no meaningful difference. They both have the same definitions of what a "knife" is, the same prohibitions, and the same exemptions.
The following is an explanation of the exemptions as explained to me by my attorney. Bear in mind that although my attorney believes in the free exercising of ones legal right to carry a knife, he also believes in erring on the side of caution. So his advice to me is not based on the belief that most cops are "cool" and will let a person slide. Instead, his advice is based on the possibility of a cop interpreting the law in a way that is least favorable to a person carrying a knife.
Work Related Purposes Exemption- If you are carrying a knife for work-related purposes, and can prove it, then it is permissible to openly carry a knife, fixed-blade or folder, with a blade 3 inches or longer in Los Angeles.
However, consider the following points-
Point 1. It's not enough to just say that you are carrying the knife "for work", like I said, you need to be able to prove it, if not right there on the street to a cop, then at least in court if you are arrested. Basically, in order for the knife to be a legitimate exemption to the length limit, you need to either be currently engaged in your job, recently engaged in your job, or directly on your way to your job, while you are carrying the knife. If your shift ended an hour ago, or if it's your day off from work, or if you live outside of LA and you are just visiting LA on vacation, don't expect the cops, or the courts, to buy your story that you were carrying the knife "for work". There needs to be a reasonable connection between your work, and your reason for carrying the knife.
Point 2. Your "work-related" reason for carrying the knife needs to reasonably match your job. For example- if you work in an office and sit at a computer all day, don't expect the cops or courts to believe that you needed to carry a big fixed-blade "for work". Again, there needs to be a reasonable connection between your work and the knife.
Recreational Purposes Exemption- If you are carrying a knife for recreational purposes, and can prove it, then it is permissible to openly carry a knife, fixed-blade or folder, with a blade 3 inches or longer in Los Angeles.
But once again, consider the following points-
Point 1. It's not enough just to say that you are carrying the knife for "recreational purposes". You need to either be actively engaged in, or on your way to, a recreational activity that might reasonably require the use of a knife with a blade 3 inches or longer. Like for example- fishing, camping, outdoor cooking, and similar activities.
Point 2. You need to be able to prove in some way that you were carrying the knife for "recreational purposes" (like having fishing/camping gear in your car). If for example you tell a cop that you were on your way to go fishing, but you have no fishing gear, and you can't name any fishing spots in LA, the cop will suspect that you are lying. Never underestimate a cops ability to detect a lie, because they have a lot of experience being lied to. And if they catch you lying, they might look for any lawful reason to arrest you (like openly carrying a knife longer than the legal limit).
Don't just expect the cops or courts to believe you, because they don't have to. And since prosecutors have their own agendas, they may very well choose not to believe you. Obey the letter of the law as best you can, cover your ass, and hopefully you will avoid trouble, or at the very least, increase your chances of beating any charges.
There is also an exemption in LA law regarding carrying a knife for "religious purposes", but since that never applied to me my attorney didn't feel it was necessary to explain it to me.
And of course, as always, my advice to people is- when in doubt about the law, consult a criminal defense attorney. You always take your chances when you use an internet forum as a source of legal information.