copy.deepcopy raises TypeError on objects with self-defined __new__() method

Question

I want to implement a symbol type, which keeps track of the symbols we already have(saved in _sym_table), and return them if they exist, or create new ones othe

Answer 1

Seems to me you want the Symbol instances to be singletons. Deepcopy, however is supposed to be used when you want an exact copy of an instance, i.e. a different instance that is equal to the original.

So the usage here kinda contradicts the purpose of deepcopy. If you want to make it work anyhow, you can define the __deepcopy__ method on Symbol.