cjm2671 cjm2671 - 5 months ago 20
Python Question

How do I use cache_clear() on python @functools.lru_cache

The documentation states:


The decorator also provides a
cache_clear()
function for clearing or
invalidating the cache.


It doesn't provide any examples or guidance on how to use
cache_clear()


I have two questions:


  • How can I run
    cache_clear()
    from a different function?

  • If I put a
    cache_clear()
    call conditionally inside the function that is being cached, will it ever get executed?


Answer

Besides caching, lru_cache decorator also adds new functions, to the decorated function - cache_info and cache_clear. Below is a simple example that should explain how they work:

>>> @lru_cache(5)
... def foo():
...     print('Executing foo...')
... 
>>> foo()
Executing foo...
>>> foo()
>>> foo.cache_info()
CacheInfo(hits=1, misses=1, maxsize=5, currsize=1)
>>> foo.cache_clear()
>>> foo()
Executing foo...

Answering your questions:

If I put a cache_clear() call conditionally inside the function that is being cached, will it ever get executed?

If the result is not cached already, the function will execute and based on your conditions, it should execute cache_clear. I wouldn't use such solution though - a good practise is to invalidate outside the cached object, otherwise you risk no invalidation at all in worst cases, unreadable code in best case.

How can I run cache_clear() from a different function?

Just import cached function and call cache_clear on it:

from x import foo

def bar():
    foo.cache_clear()
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