Check if variable is set to NO_VALUE

Question

I am using dogpile to have cache in my python program. During the init of my program, I clean the cache SimpleCache.set_fault_injector(NO_VALUE)

@staticmethod
def set_fault_injector(injector):
    SimpleCache.save("fault_injector", injector)

Then I retrieve the object with:

@staticmethod
def get_fault_injector():
    return SimpleCache.get("fault_injector")

injector = get_fault_injector()

Here in my test, I am checking if the injector variable is set to NO_VALUE, but the comparison is returning False (it should be TRUE). How do I check if injector is set to NO_VALUE? The way that I clear the cache is correct?

In [3]: injector
Out[3]: <dogpile.cache.api.NoValue at 0x7fdde0dfd750>

In [4]: NO_VALUE
Out[4]: <dogpile.cache.api.NoValue at 0x7fdde16dbed0>

In [5]: injector == NO_VALUE
Out[5]: False

In [6]: type(injector)
Out[6]: dogpile.cache.api.NoValue

In [7]: type(NO_VALUE)
Out[7]: dogpile.cache.api.NoValue

In [8]: injector is NO_VALUE
Out[8]: False

[9]: type(injector) == type(NO_VALUE)
Out[9]: True

Answer 1

I don't have experience in dogpile, however, from what I understand from the docs, when a value is missing then dogpile normally returns a specific instance of dogpile.cache.api.NoValue, which is NO_CACHE.

The issue here is probably linked to you explicitly setting a cache key to NO_CACHE, which somehow ends up leaving you with 2 different instances of the NoValue class.

It appears to me that NO_CACHE is not really meant to be used for unsetting a key, I believe your issue would be resolved if you actually used .delete("fault_injector") or whatever removal method your cache wrapper has available.