[Python-Dev] PEP 492: async/await in Python; v3 (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Thu Apr 30 00:46:16 CEST 2015

Yury Selivanov wrote:

Won't that prevent some existing generator-based coroutines (ones not decorated with @coroutine) from calling ones implemented with 'async def'?

It would. But that's not a backwards compatibility issue.

It seems to go against Guido's desire for the new way to be a 100% drop-in replacement for the old way. There are various ways that old code can end up calling new code -- subclassing, callbacks, etc.

It also means that if person A writes a library in the new style, then person B can't make use of it without upgrading all of their code to the new style as well. The new style will thus be "infectious" in a sense.

I suppose it's up to Guido to decide whether it's a good or bad infection. But the same kind of reasoning seemed to be at least partly behind the rejection of PEP 3152.

-- Greg

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