[New-bugs-announce] [issue42903] optimize lru_cache for functions with no arguments

[Eugene Toder]

New submission from Eugene Toder <eltoder at gmail.com>:

It's convenient to use @lru_cache on functions with no arguments to delay doing some work until the first time it is needed. Since @lru_cache is implemented in C, it is already faster than manually caching in a closure variable. However, it can be made even faster and more memory efficient by not using the dict at all and caching just the one result that the function returns.

Here are my timing results. Before my changes:

$ ./python -m timeit -s "import functools; f = functools.lru_cache()(lambda: 1)" "f()"
5000000 loops, best of 5: 42.2 nsec per loop
$ ./python -m timeit -s "import functools; f = functools.lru_cache(None)(lambda: 1)" "f()"
5000000 loops, best of 5: 38.9 nsec per loop

After my changes:

$ ./python -m timeit -s "import functools; f = functools.lru_cache()(lambda: 1)" "f()"
10000000 loops, best of 5: 22.6 nsec per loop

So we get improvement of about 80% compared to the default maxsize and about 70% compared to maxsize=None.

----------
components: Library (Lib)
messages: 384883
nosy: eltoder, serhiy.storchaka, vstinner
priority: normal
severity: normal
status: open
title: optimize lru_cache for functions with no arguments
type: performance
versions: Python 3.10

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42903>
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