Sample lru dict impl

lrudict.py

import collections
from typing import Optional, TypeVar, ContextManager, Generic, Any, MutableMapping


class LRUDict(collections.OrderedDict, MutableMapping[_KT, _VT]):
    def __init__(self, max_size: Optional[int] = None, min_size: int = 0):
        super().__init__()
        self.min_size = min_size
        self.max_size = max_size
        if self.max_size and self.max_size < self.min_size:
            raise ValueError(f'`max_size` cannot be smaller than `min_size` ({self.min_size})')

    def __setitem__(self, key, value):
        if self.max_size and len(self) >= self.max_size and key not in self:
            self.evict_oldest()
            oldest = next(iter(self))
            del self[oldest]
        return super().__setitem__(key, value)

    def __getitem__(self, key):
        if key in self:
            self.move_to_end(key, last=True)
        return super().__getitem__(key)

    def evict_oldest(self):
        if len(self) > self.min_size:
            oldest = next(iter(self))
            del self[oldest]