Dictionary 中的哪些键值未更新？

Question

I have a dictionary whose keys are integers and values are lists, for each key list is updated in every iteration. Also new keys are added. But there may be situations where some key values are not updated.

whats the most efficient way to know which keys were not updated?

I can iterate all lists in dictionary and check from length if that list was updated or not but is there a better way?

Note: Integer Keys are not consecutive numbers. Therefore using simple lists or arrays does not seem like an option

Answer 1

As an alternative to the solution @Scott Skiles made in a comment, I would add a value to the dictionary, next to the list, that designates the most recent iteration when the key was modified:

my_dict = {}
iteration_num = 0
while True:
    updates_to_make = some_function_producing_2tuples()
    # iterate through new additions, and add them to the list
    for key, value in updates_to_make:
        # the 'value' in my_dict is a 2-tuple (last_updated, list)
        # we replace last_updated every time we change the key somehow
        if key in my_dict:
            my_dict[key][1].append(value)
            my_dict[key][0] = iteration_num
        else:
            my_dict[key] = (iteration_num, [value])
    ...
    iteration_num += 1

You can then figure out which keys are or are not updated by applying a filter:

updated_keys = [k for k, v in my_dict.items() if v[0] == iteration_num]