Python functools lru_cache with class methods: release object

This is not the cleanest solution, but it's entirely transparent to the programmer:

import functools
import weakref

def memoized_method(*lru_args, **lru_kwargs):
    def decorator(func):
        @functools.wraps(func)
        def wrapped_func(self, *args, **kwargs):
            # We're storing the wrapped method inside the instance. If we had
            # a strong reference to self the instance would never die.
            self_weak = weakref.ref(self)
            @functools.wraps(func)
            @functools.lru_cache(*lru_args, **lru_kwargs)
            def cached_method(*args, **kwargs):
                return func(self_weak(), *args, **kwargs)
            setattr(self, func.__name__, cached_method)
            return cached_method(*args, **kwargs)
        return wrapped_func
    return decorator

It takes the exact same parameters as lru_cache, and works exactly the same. However it never passes self to lru_cache and instead uses a per-instance lru_cache.

I will introduce methodtools for this use case.

pip install methodtools to install https://pypi.org/project/methodtools/

Then your code will work just by replacing functools to methodtools.

from methodtools import lru_cache
class Foo:
    @lru_cache(maxsize=16)
    def cached_method(self, x):
        return x + 5

Of course the gc test also returns 0 too.