On Fri, Dec 15, 2017 at 12:45 PM, Raymond Hettinger < raymond.hettin...@gmail.com> wrote:
> > > On Dec 15, 2017, at 7:53 AM, Guido van Rossum <gu...@python.org> wrote: > > > > Make it so. "Dict keeps insertion order" is the ruling. > > On Twitter, someone raised an interesting question. > > Is the guarantee just for 3.7 and later? Or will the blessing also cover > 3.6 where it is already true. > > The 3.6 guidance is to use OrderedDict() when ordering is required. As of > now, that guidance seems superfluous and may no longer be a sensible > practice. For example, it would be nice for Eric Smith when he does his > 3.6 dataclasses backport to not have to put OrderedDict back in the code. > For 3.6 we can't change the language specs, we can just document how it works in CPython. I don't know what other Python implementations do in their version that's supposed to be compatible with 3.6 but I don't want to retroactively declare them non-conforming. (However for 3.7 they have to follow suit.) I also don't think that the "it stays ordered across deletions" part of the ruling is true in CPython 3.6. I don't know what guidance to give Eric, because I don't know what other implementations do nor whether Eric cares about being compatible with those. IIUC micropython does not guarantee this currently, but I don't know if they claim Python 3.6 compatibility -- in fact I can't find any document that specifies the Python version they're compatible with more precisely than "Python 3". -- --Guido van Rossum (python.org/~guido)
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