PEP 236 states that the intention of the proposed feature is to allow modules "to request that the code in module M use the new syntax or semantics in the current release C".

It achieves this by introducing a new statement, the future_statement. This looks like an import statement, but isn't. The PEP author admits that 'overloading "import" does suck'. I agree (not surprisingly, since Tim added this QA item after we discussed it in email).

It also says "But if we introduce a new keyword, that in itself would break old code". Here I disagree, and I propose patch 404997 as an alternative (https://sourceforge.net/tracker/index.php?func=detail&aid=404997&gro...)

<specification section="Alternative Solution"> In essence, with that patch, you would write

directive nested_scopes

instead of

from __future__ import nested_scopes

This looks like as it would add a new keyword directive, and thus break code that uses "directive" as an identifier, but it doesn't. In this release, "directive" is only a keyword if it is the first keyword in a file (i.e. potentially after a doc string, but not after any other keyword). So

class directive: def __init__(self, directive): self.directive = directive

continues to work as it did in previous releases (it does not even produce a warning, but could if desired). Only when you do

directive nested_scopes directive braces class directive: def __init__(self, directive): self.directive = directive

you get a syntax error, since "directive" is then a keyword in that module.

The directive statement has a similar syntax to the C #pragma "statement", in that each directive has a name and an optional argument. The choice of the keyword "directive" is somewhat arbitrary; it was deliberately not "pragma", since that implies an implementation-defined semantics (which directive does not have).

In terms of backwards compatibility, it behaves similar to "from __future__ import ...": older releases will give a SyntaxError for the directive syntax (instead of an ImportError, which a __future__ import will give). "Unknown" directives will also give a SyntaxError, similar to the ImportError from the __future__ import. </specification>

Please let me know what you think. If you think this should be written down in a PEP, I'd request that the specification above is added into PEP 236.

Regards, Martin