Изменяемая коллекция, которая может выступать в качестве ключа словаря

Условие

Create a mutable container (for instance, a list‑like structure) whose objects are eligible to be used as keys in a Python dict.

# TODO: создать собственный класс, экземпляры которого можно использовать как ключи

Ответ

Use identity-based equality and hashing, while keeping mutable contents in an attribute. Changing the contents then does not change the dictionary key's identity.

class MutableContainer:
    def __init__(self, items=()):
        self.items = list(items)

    def append(self, value):
        self.items.append(value)

    def __iter__(self):
        return iter(self.items)

    def __getitem__(self, index):
        return self.items[index]

key = MutableContainer([1])
lookup = {key: 'value'}
key.append(2)
assert lookup[key] == 'value'

The class inherits object equality and hashing, so two containers with equal contents remain distinct keys. Do not calculate a hash from mutable contents: modifying them could make an existing dictionary entry unreachable. Value-based keys should instead use an immutable snapshot, such as a tuple.