On 27 November 2017 at 06:29, Nathaniel Smith <njs at pobox.com> wrote: > - In async/await, it's not obvious how to write leaf functions: > 'await' is equivalent to 'yield from', but there's no equivalent to > 'yield'. You have to jump through some hoops by writing a class with a > custom __await__ method or using @types.coroutine. Of course it's > doable, and it's no big deal if you're writing a proper async library, > but it's awkward for quick ad hoc usage. > > For a concrete example of 'ad hoc coroutines' where I think 'yield > from' is appropriate, here's wsproto's old 'yield from'-based > incremental websocket protocol parser: > > https://github.com/python-hyper/wsproto/blob/4b7db502cc0568ab2354798552148dadd563a4e3/wsproto/frame_protocol.py#L142 sys.set_coroutine_wrapper itself is another case where you genuinely *can't* rely on async/await in the wrapper implementation. The current example shown at https://docs.python.org/3/library/sys.html#sys.set_coroutine_wrapper is of a case that will *fail*, since it would otherwise result in infinite recursion when the coroutine wrapper attempts to call the coroutine wrapper. Cheers, Nick. P.S. Making that point reminded me that I still haven't got around to updating those docs to also include examples of how to do it *right*: https://bugs.python.org/issue30578 -- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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