LRUCache.py

class LRUCache:
    def __init__(self, max_size):
        self.dict = OrderedDict()
        self.max_size = max_size

    def __len__(self):
        return len(self.dict)

    def __contains__(self, key):
        if key in self.dict:
            self.dict.move_to_end(key, last=False)  # Move to beginning
            return True
        return False

    def __setitem__(self, key, value):
        self.dict[key] = value
        self.dict.move_to_end(key, last=False)      # Move to beginning
        if len(self) > self.max_size:
            self.dict.popitem(last=True)            # Pop the last key

    def __getitem__(self, key):
        val = self.dict.get(key)
        if val is not None:
            self.dict.move_to_end(key, last=False)  # Move to beginning
        return val