Using Functools.lru_cache On Functions With Constant But Non-hashable Objects

Is it possible to use functools.lru_cache for caching a partial function created by functools.partial? My problem is a function that takes hashable parameters and contant, non-hash

Solution 1:

As the array is constant you can use a wrapper around the actual lru cached function and simply pass the key value to it:

from functools import lru_cache, partial
import numpy as np


def lru_wrapper(array=None):
    @lru_cache(maxsize=None)
    def foo(key):
        return '%s:' % key, array
    return foo


arr = np.array([1, 2, 3])
func = lru_wrapper(array=arr)

for x in [0, 0, 1, 2, 2, 1, 2, 0]:
    print (func(x))

print (func.cache_info())

Outputs:

('0:', array([1, 2, 3]))
('0:', array([1, 2, 3]))
('1:', array([1, 2, 3]))
('2:', array([1, 2, 3]))
('2:', array([1, 2, 3]))
('1:', array([1, 2, 3]))
('2:', array([1, 2, 3]))
('0:', array([1, 2, 3]))
CacheInfo(hits=5, misses=3, maxsize=None, currsize=3)

Solution 2:

Here is an example of how to use lru_cache with functools.partial:

from functools import lru_cache, partial
import numpy as np


def foo(key, array):
    return '%s:' % key, array


arr = np.array([1, 2, 3])
pfoo = partial(foo, array=arr)
func = lru_cache(maxsize=None)(pfoo)

for x in [0, 0, 1, 2, 2, 1, 2, 0]:
    print(func(x))

print(func.cache_info())

Output:

('0:', array([1, 2, 3]))
('0:', array([1, 2, 3]))
('1:', array([1, 2, 3]))
('2:', array([1, 2, 3]))
('2:', array([1, 2, 3]))
('1:', array([1, 2, 3]))
('2:', array([1, 2, 3]))
('0:', array([1, 2, 3]))
CacheInfo(hits=5, misses=3, maxsize=None, currsize=3)

This is more concise than solution of @AshwiniChaudhary, and also uses the functools.partial following the OP's requirement.

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