So… I think what you’re asking generally here is whether you’re doing copyright infringement. You can read all you want about it if you query your favorite seach engine with these keywords. Maybe see Which license for small scripts ? also.
I don’t know about blenderartists’s stance on copyright in the author posts, but you can check the one on stackexchange by clicking on the timeline button.
https://blender.stackexchange.com/posts/6873/timeline this one is CC BY-SA 3.0
Although it would be pretty hard for the authors of these lines of code to go to courts against you for basically using public knowledge code readily available in the official API docs and a million other places on the internet.
If you want to credit the authors, there are official guidelines available online for how to do so.
Do bear in mind that you can sell access to your addon, but you won’t be able to stop anyone from redistributing it for free (if they also comply with the license by acknowledging your copyright) if you want to comply with the GPL license.