Custom LRU cache implementation that gives access to the underlying cache dictionary.

lru_cache.py

def lru_cache(maxsize=0):
    """Custom LRU cache implementation that gives access to the underlying cache dictionary. [better to used functools one if you don't need this]"""
    def wrap(f):
        cache = {}
        last_used = []

        def wrapped(*args):
            if args in cache:
                # HIT.
                # Update the last_used list.
                if last_used[0] != args:
                    i = last_used.index(args)
                    last_used.insert(0, last_used.pop(i))
                assert set(cache) == set(last_used)
                return cache[args]
            # MISS.
            out = f(*args)
            cache[args] = out
            last_used.insert(0, args)
            if maxsize > 0 and len(cache) > maxsize:
                cache.pop(last_used[-1], None)
                del last_used[-1]
            assert set(cache) == set(last_used)
            return out

        wrapped._cache = cache
        wrapped._last_used = last_used
        return wrapped
    return wrap


def test_lru_cache():
    _calls = []

    def f(x):
        _calls.append(x)
        return x * x
    fc = lru_cache(maxsize=3)(f)

    assert fc(2) == 4
    assert len(_calls) == 1
    assert fc._cache == {(2,): 4}
    assert fc._last_used == [(2,)]

    assert fc(2) == 4
    assert len(_calls) == 1

    assert fc(3) == 9
    assert len(_calls) == 2
    assert fc._cache == {(2,): 4, (3,): 9}
    assert fc._last_used == [(3,), (2,)]

    assert fc(4) == 16
    assert len(_calls) == 3
    assert fc._cache == {(2,): 4, (3,): 9, (4,): 16}
    assert fc._last_used == [(4,), (3,), (2,)]

    assert fc(5) == 25
    assert len(_calls) == 4
    assert fc._cache == {(3,): 9, (4,): 16, (5,): 25}
    assert fc._last_used == [(5,), (4,), (3,)]

    assert fc(3) == 9
    assert len(_calls) == 4
    assert fc._cache == {(3,): 9, (4,): 16, (5,): 25}
    assert fc._last_used == [(3,), (5,), (4,)]

    assert fc(2) == 4
    assert len(_calls) == 5
    assert fc._cache == {(3,): 9, (5,): 25, (2,): 4}
    assert fc._last_used == [(2,), (3,), (5,)]