Antoine Pitrou wrote:
On Fri, 26 Aug 2011 17:25:56 -0700
Dan Stromberg <drsali...@gmail.com> wrote:
[...]
If you add regex as "import regex", and the new regex module doesn't work
out, regex might be harder to get rid of. from __future__ import is an
established way of trying something for a while to see if it's going to
work.
That's an interesting idea. This way, integrating the new module would
be a less risky move, since if it gives us too many problems, we could
back out our decision in the next feature release.
I'm not sure that's correct. If there are differences in either the
interface or the behaviour between the new regex and re, then reverting
will be a pain regardless of whether you have:
from __future__ import re
re.compile(...)
or
import regex
regex.compile(...)
Either way, if the new regex library goes away, code will break, and
fixing it may not be easy. It's not likely to be so easy that merely
deleting the "from __future__ ..." line will do it, but if it is that
easy, then using "import re as regex" will be just as easy.
Have then been any __future__ features that were added provisionally? I
can't think of any. That's not what __future__ is for, at least
according to PEP 236.
http://www.python.org/dev/peps/pep-0236/
I can't think of any __future__ feature that could be easily reverted
once people start relying on it. Either syntax would break, or behaviour
would change.
The PEP even explicitly states that __future__ should not be used for
changes which are backward compatible:
Note that there is no need to involve the future_statement machinery
in new features unless they can break existing code; fully backward-
compatible additions can-- and should --be introduced without a
corresponding future_statement.
I wasn't around for the move from 1.4 regex to 1.5 re, so I don't know
what was done poorly last time. But I can't see why we should treat
regular expressions so differently from (say) argparse and optparse.
from __future__ import optparse
No. Just... no.
--
Steven
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