[issue28991] Fix obscure lru_cache reentrancy bug

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Wrapping len() in an lru_cache is bad idea, because this brakes len() of lists, dicts and other non-hashable collections.

Should we support this doubtful case?

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28991>
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