Second version of the custom cache function won't work if we have duplicate arguments.

[amirsoroush]

Hi Fred.
At the end of the file Part 3/Section 05 - Sets/06 - Frozen Sets.ipynb, we created a custom function for memoization replacing the lru_cache.

The second version of it is:

We can even tweak this to effectively provide more efficient caching when the order of positional arguments is not important either:

def memoizer(fn):
    cache = {}
    def inner(*args, **kwargs):
        key = frozenset(args) | frozenset(kwargs.items())
        if key in cache:
            return cache[key]
        else:
            result = fn(*args, **kwargs)
            cache[key] = result
            return result
    return inner

@memoizer
def adder(*args):
    print('calculating...')
    return sum(args)

I just wanted to note that this cache mechanism won't work if we have duplicate arguments. That set (frozenset actually) removes the duplicate arguments.

Take a look at this example:

print(adder(1, 2, 2))
print(adder(1, 1, 2))  # 5 !!

You may add a note that arguments should be different for this to work.
Thanks.

[fbaptiste]

Good point!