Making a list subclass hashable

Question

I want to derive a class from list, add a few instance attributes to it, and make it hashable. What is a good (fast and neat) way to do it?

UPDATE:

I deleted a lengthy explanation of a use case. I also moved a related but separate issue into a different question.

Answer 1

This code is fine. You're making a copy of the list, which could be a bit slow.

def __hash__(self):
    return hash(tuple(self.list_attribute))

You have several options if you want to be faster.

• Store list_attribute as a tuple, not a list (after it is fully constructed)
• Compute the hash once at init time and store the hash value. You can do this because your class is immutable, so the hash will never change.
• Write your own hash function. Here's the hash function for tuple, do something similar.