An ordered dictionnary kind of like a Deque: adding or updating a key (re)-appends it to the end of the dictionary, and if the dictionary is full, the oldest elements are pop'ed (in a FIFO fashion)

OrderedDequeDict.py

class OrderedDequeDict(OrderedDict):

    def __init__(self, size=100, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.size = size

    def __setitem__(self, key, value):
        if key in self:
            del self[key]
        elif len(self) == self.size:
            self.popitem(last=False)

        OrderedDict.__setitem__(self, key, value)