[Python-Dev] PEP 408 -- Standard library __preview__ package

Stephen J. Turnbull turnbull at sk.tsukuba.ac.jp
Sat Jan 28 05:44:52 CET 2012

Michael Foord writes:

 > >> Assuming the module is then promoted to the the standard library proper in
 > >> release ``3.X+1``, it will be moved to a permanent location in the library::
 > >>
 > >>      import example
 > >>
 > >> And importing it from ``__preview__`` will no longer work.
 > > Why not leave it accessible through __preview__ too?
 > +1

Er, doesn't this contradict your point about using

    from __preview__ import spam
except ImportError:
    import spam


I think it's a bad idea to introduce a feature that's *supposed* to
break (in the sense of "make a break", ie, change the normal pattern)
with every release and then try to avoid breaking (in the sense of
"causing an unexpected failure") code written by people who don't want
to follow the discipline of keeping up with changing APIs.  If they
want that stability, they should wait for the stable release.

Modules should become unavailable from __preview__ as soon as they
have a stable home.

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