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

Michael Foord fuzzyman at voidspace.org.uk
Fri Jan 27 16:25:28 CET 2012

On 27/01/2012 14:37, Philippe Fremy wrote:
> Hi,
> A small comment from a user perspective.
> Since a package in preview is strongly linked to a given version of
> Python, any program taking advantage of it becomes strongly specific to
> a given version of Python.
> Such programs will of course break for any upgrade or downgrade of
> python version. To make the reason for the breakage more explicit, I
> believe that the PEP should provide examples of correct versionned usage
> of the module.
> Something along the lines of :
> if sys.version_info[:2] == (3, X):
> 	from __preview__ import example
> else:
> 	raise ImportError( 'Package example is only available as preview in
> Python version 3.X. Please check the documentation of your version of
> Python to see if and how you can get the package example.' )

A more normal incantation, as is often the way for packages that became 
parts of the standard library after first being a third party library 
(sometimes under a different name, e.g. simplejson -> json):

     from __preview__ import thing
except ImportError:
     import thing

So no need to target a very specific version of Python.


> cheers,
> Philippe
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