Need python dictionary to act like deque (have maximum length)

Question

Is there any builtin (or very simple) method of having a python dictionary work in a similar fashion as deque.

I need it to have a maximum size, and when new keys are added, if the maximum length is reached then the key added first is deleted. It shouldn't be too difficult to implement as a custom class, but using builtins is always prefered.

I am using Python 3.6 if that is of any help.

Answer 1

It sounds like a variant of OrderedDict.

class FixSizeOrderedDict(OrderedDict):
    def __init__(self, *args, max=0, **kwargs):
        self._max = max
        super().__init__(*args, **kwargs)

    def __setitem__(self, key, value):
        OrderedDict.__setitem__(self, key, value)
        if self._max > 0:
            if len(self) > self._max:
                self.popitem(False)

Answer 2

It sounds like you want a least recently used (LRU) cache.

The functools.lru_cache decorator might be useful to you. If you want more control, then check out the package pylru or just google Python LRU cache.