What are some (concrete) use-cases for metaclasses?

Question

I have a friend who likes to use metaclasses, and regularly offers them as a solution.

I am of the mind that you almost never need to use metaclasses. Why? because I

Answer 1

Some GUI libraries have trouble when multiple threads try to interact with them. tkinter is one such example; and while one can explicitly handle the problem with events and queues, it can be far simpler to use the library in a manner that ignores the problem altogether. Behold -- the magic of metaclasses.

Being able to dynamically rewrite an entire library seamlessly so that it works properly as expected in a multithreaded application can be extremely helpful in some circumstances. The safetkinter module does that with the help of a metaclass provided by the threadbox module -- events and queues not needed.

One neat aspect of threadbox is that it does not care what class it clones. It provides an example of how all base classes can be touched by a metaclass if needed. A further benefit that comes with metaclasses is that they run on inheriting classes as well. Programs that write themselves -- why not?