I just finished the work on Moon, a library for Lua 5.3 that provides a class system along with the corresponding functions inspired by the one of Python. It supports multiple inheritance by using a MRO, operator overloading, properties and metaclasses. However, it is rather optimized on flexibility than performance since creating a lightweight class system ought not to be troublesome in Lua.
I recommend just using it when you already know what OOP means in general but not necessarily in Python. I included an introduction of the concepts that are not present in the most common OO languages in the documentation.
You can download it from github or pastebin (id: RgzJxwVF). If you encounter bugs, please report them on github. The documentation is on github as well. I hope it is able to clear all your questions. An example can also be found on pastebin (id: sxrQPdjL).
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