> On Apr 26, 2020, at 7:03 AM, Tom Forbes <t...@tomforb.es> wrote:
>
> I would like to suggest adding a simple “once” method to functools. As the
> name suggests, this would be a decorator that would call the decorated
> function, cache the result and return it with subsequent calls.
It seems like you would get just about everything you want with one line:
once = lru_cache(maxsize=None)
which would be used like this:
@once
def welcome():
len('hello')
> Using lru_cache like this works but it’s not as efficient as it could be - in
> every case you’re adding lru_cache overhead despite not requiring it.
You're likely imagining more overhead than there actually is. Used as shown
above, the lru_cache() is astonishingly small and efficient. Access time is
slightly cheaper than writing d[()] where d={(): some_constant}. The
infinite_lru_cache_wrapper() just makes a single dict lookup and returns the
value.¹ The lru_cache_make_key() function just increments the empty args tuple
and returns it.² And because it is a C object, calling it will be faster than
for a Python function that just returns a constant, "lambda: some_constant()".
This is very, very fast.
Raymond
¹ https://github.com/python/cpython/blob/master/Modules/_functoolsmodule.c#L870
² https://github.com/python/cpython/blob/master/Modules/_functoolsmodule.c#L809
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