问题
I have been trying to make functools.lru_cache
instance specific as described in this answer, but their solution fails when used on the __call__
method.
class test:
def __init__(self):
self.method = lru_cache()(self.method)
self.__call__ = lru_cache()(self.__call__)
def method(self, x):
print('method', end=' ')
return x
def __call__(self, x):
print('__call__', end=' ')
return x
b = test()
# b.method is cached as expected
print(b.method(1)) # method 1
print(b.method(1)) # 1
# __call__ is executed every time
print(b(1)) # __call__ 1
print(b(1)) # __call__ 1
So the results of __call__
are not getting cached when wrapped using this method. The cache on __call__
does not even register the function having been called, and unhashable values do not throw errors.
print(b.method.cache_info())
# CacheInfo(hits=1, misses=1, maxsize=128, currsize=1)
print(b.__call__.cache_info())
# CacheInfo(hits=0, misses=0, maxsize=128, currsize=0)
print(b.call({})) # __call__ {}
print(b.method({})) # ... TypeError: unhashable type: 'dict'
回答1:
This is due to the difference between class attributes and instance attributes. When accessing an attribute (such as method
) python first checks for an instance attribute. If you have not assigned to self.method
it will not find one. Then class attributes are checked, which is equivalent to self.__class__.method
. The value of this function is not changed by assigning to self.method
, that only updates the instance attribute.
However, b(1)
becomes b.__class__.__call__(b, 1)
which uses the original class definition of __call__
and b.__call__(1)
will be cached the same way as method
since it uses the instance definition.
回答2:
The original answer is really good.
I am attaching another solution of the problem.
methodtools.lru_cache
will work as you expect.
from methodtools import lru_cache
class test:
@lru_cache
def __call__(self, x):
print('__call__', end=' ')
return x
It requires to install methodtools
via pip:
pip install methodtools
来源:https://stackoverflow.com/questions/53423121/why-does-functools-lru-cache-not-cache-call-while-working-on-normal-methods