protecting app I've written

I've written a small app with python/wxpython and would like to sell it.

I'm looking for help and advice on adding a software key or copy protection.My app is targeted at a fairly small industry group and 开发者_运维百科wouldn't want most of my target market to just copy it from a friend who bought it.

I've seen post about buying third party software to cover this but I'm not sure if that would make financial sense as I'm not going to ask much or make a lot off of my product but would like to make something for my efforts. I'm a newbie at this, and am not sure if it is just to difficult an effort to try to write something like that myself.