[Python-Dev] PEP 414

[Ned Batchelder]

On 2/26/2012 6:14 AM, Nick Coghlan wrote:
> As soon as you allow the use of "from __future__ import
> unicode_literals" or a module level "__metaclass__ = type", you can't
> review diffs in isolation any more - whether the diff is correct or
> not will depend on the presence or absence of module level tweak to
> the language semantics.
>
> Future imports work well for things like absolute imports, new
> keywords, or statements becoming functions - if the future import is
> missing when you expected it to be present (or vice-versa) will result
> in a quick SyntaxError or ImportError that will point you directly to
> the offending code. Unicode literals and implicitly creating new-style
> classes are a different matter - for those, if the module level
> modification takes place (or doesn't take place when you expected it
> to be there), you get unexpected changes in behaviour instead of a
> clear exception that refers directly to the source of the problem.
There are already __future__ imports that violate this principle:  from 
__future__ import division.  That doesn't mean I'm in favor of this new 
__future__, just keeping a wide angle on the viewfinder.

--Ned.