Ability to use lru_cache(user_function) was only introduced in Python 3.8.
Buster has Python 3.7. This causes startup failure in Buster. Fix this by using
the older API for lru_cache instead of the new one.
Tests:
- On stable and testing, starting the Plinth daemon and visiting the performance
page should work.
- Adding a print statement in the _get_url() method shows that it is only called
once, ever.
Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>
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