[New-bugs-announce] [issue38565] Expose the value passed of typed passed to functools.lru_cache

[Scott Sanderson]

New submission from Scott Sanderson <scoutoss at gmail.com>:

In some circumstances, it's useful to be able in inspect the parameters with which an instance of functools.lru_cache was instantiated. It's currently possible to recover the cache's maxsize via the .cache_info() method, but there's no way to recover the value passed for `typed`, which controls whether the lru_cache's cache is partitioned by input type.

This came up in the context of cloudpickle, a library that tries to extend pickle to support more types (in particular, interactively-defined functions and classes) for use-cases like cluster computing. 

It's currently not possible to pickle an lru-cache decorated function that's defined in __main__ (which includes, e.g. a Jupyter Notebook). We can **almost** fix this with a pure library solution (see https://github.com/cloudpipe/cloudpickle/pull/309), but we're currently blocked by the fact that there's no way to recover the value that was passed for `typed`. Exposing a .typed attribute on the extension type for lru_cached functions fixes this

For more discussion, see the above linked PR, along with https://github.com/cloudpipe/cloudpickle/issues/178.

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components: Library (Lib)
messages: 355226
nosy: Scott Sanderson2
priority: normal
severity: normal
status: open
title: Expose the value passed of typed passed to functools.lru_cache
type: enhancement
versions: Python 3.9

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<https://bugs.python.org/issue38565>
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