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.
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