On Wed, 29 Apr 2020 12:01:24 -0700 Raymond Hettinger <raymond.hettin...@gmail.com> wrote: > > The call_once() decorator would need different logic: > > 1) if the function has already been called and result is known, return the > prior result :-) > 2) if function has already been called, but the result is not yet known, > either block or fail :-(
It definitely needs to block. > 3) call the function, this cannot be reentrant :-( Right. The typical use for such a function is lazy initialization of some resource, not recursive computation. > 4) record the result for future calls. > [...] > > Would it fair to describe call_once() like this? > > call_once() is just like lru_cache() but: > > 1) guarantees that a function never gets called more than once > 2) will block or fail if a thread-switch happens during a call Definitely block. > 3) only works for functions that take zero arguments > 4) only works for functions that can never be reentrant > 5) cannot make the one call guarantee across multiple processes > 6) does not have instrumentation for number of hits > 7) does not have a clearing or reset mechanism Clearly, instrumentation and a clearing mechanism are not necessary. They might be "nice to have", but needn't hinder initial adoption of the API. Regards Antoine. _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/NZ2VDB4WDPXP44NGZEXW2ACE424ODFBH/ Code of Conduct: http://python.org/psf/codeofconduct/
