Python get the cache dictionary of _lru_cache_wrapper object

I have this simple cache decorator demo here

@functools.cache
def cached_fib(n):
    assert n > 0
    if n <= 2:
        return 1
    return cached_fib(n - 1) + cached_fib(n - 2)

t1 = time.perf_counter()
cached_fib(400)
t2 = time.perf_counter()
print(f"cached_fib: {t2 - t1}")    # 0.0004117000003134308

I want to access the actual cache dictionary object inside this cached_fib, but when I try to access through cached_fib.cache, it gives me an error saying that AttributeError: 'functools._lru_cache_wrapper' object has no attribute 'cache' though the cache attribute is used in python and c version alike.

Thank you!

Solution

The internals of the cache are encapsulated for thread safety and to allow the underlying implementation details to change.

The three public attributes are, some statistics in cache_info:

>>> cached_fib.cache_info()
CacheInfo(hits=0, misses=0, maxsize=None, currsize=0)
>>> cached_fib(123)
22698374052006863956975682
>>> cached_fib.cache_info()
CacheInfo(hits=120, misses=123, maxsize=None, currsize=123)

Details about the init mode in cache_parameters

>>> cached_fib.cache_parameters()
{'maxsize': None, 'typed': False}

And cache_clear which purges the cache.

>>> cached_fib.cache_info()
CacheInfo(hits=120, misses=123, maxsize=None, currsize=123)
>>> cached_fib.cache_clear()
>>> cached_fib.cache_info()
CacheInfo(hits=0, misses=0, maxsize=None, currsize=0)

Additionally, the "uncached" function version is publicly available via __wrapped__, but this is not something specific to functools.cache:

>>> cached_fib
<functools._lru_cache_wrapper object at 0x10b7a3270>
>>> cached_fib.__wrapped__
<function cached_fib at 0x10bb781f0>

If you want a cache implementation where the underlying dict is exposed to the user, I recommend the third-party cachetools library.