Exceptions are cached?

Hello,

I’m seeing some weird thing with Exception… The lru_cache decorator would not cache anything in case an exception is raised, so something like this:

# not very useful but shows well the difference
foo = 0
@lru_cache(maxsize=10)
def return_something_sync(a):
    global foo
    foo += 1
    raise Exception(foo, time.time())

Would raise something like this:

return_something_sync(1)
>>> Exception: (1, 1564754537.844053)
return_something_sync(1)
>>> Exception: (2, 1564754539.949204)

So a new exception each time. But with alru_cache, the exception itself is cached and raised back!

foo = 0
@alru_cache(maxsize=10)
async def return_something(a):
    global foo
    foo += 1
    raise Exception(foo, time.time())

Will raise:

await return_something(1)
>>> Exception: (1, 1564754484.767096)
await return_something(1)
>>> Exception: (1, 1564754484.767096)

I would expect the exception not to be kept in cache, like for the sync equivalent; otherwise we have basically no way to call again the same function in case of transient issue (which can frequently happen if involving network access…).

Or am I missing something?

Thanks

[GrazingScientist]

OK… and then after I read the code, and see that there is a cache_exceptions option to turn that off!

Anyway, shouldn’t that option be False by default to be consistent with the sync version?

Totally agree! Thank you for mentioning this parameter! 😃

This parameter (or at least this behaviour of caching exceptions) should be mentioned in the README!

[RouquinBlanc]

OK… and then after I read the code, and see that there is a cache_exceptions option to turn that off!

Anyway, shouldn’t that option be False by default to be consistent with the sync version?