[Python-Dev] Add from __experimental__ import bla [was: Should we move to replace re with regex?]

[exarkun at twistedmatrix.com]

On 07:57 pm, digitalxero at gmail.com wrote:
>In the thread about replacing re with regex someone mentioned adding
>to __future__ which isnt a great idea as future APIs are already
>solidified, they just live there to give developer time to adapt their
>code. The idea of a __experimental__ area is good for any pep's or
>stliib additions that are somewhat controversial (API isnt agreed on,
>code may take a while to integrate properly, developer wants some time
>to hash out any edge case bugs or API clarifications that may come up
>in large scale testing, etc).
>
>__experimental__ should emit a warning on import that says anything in
>here may change or be removed at any time and should not be used in
>stable code.
>
>__experimental__ features should behave the same as __future__ in that
>they can add new keywords or semantics to the existing language
>
>__experimental__ features can move directly to the stlib or builtins
>if they do not add new keywords and/or are backwards compatible with
>the feature they are replacing. Otherwise they move into __future__
>for how ever many releases are deemed reasonable time for developers
>to adapt their code.

Hi Dj,

As a developer of Python libraries and applications, I don't see how 
this would make my life easier.

A warning in a module docstring that a module may not be long-lived if 
it is not well received tells me just as much as a warning emitted at 
runtime.  And a warning emitted at runtime is likely to scare my users 
into thinking something is broken, leading to spurious or misleading bug 
reports.  There also does not appear to be general consensus that 
modules should be added to stdlib if they are not widely used and 
demanded, so I don't know when a module would be added to 
__experimental__, anyway.  The normal deprecation procedures (rarely 
used as they are) seem to cover this, anyway.

Adding a new namespace separate from __future__ also just gives me 
another thing to remember.  Was the feature added to __experimental__ or 
__future__?  Also, it seems even less common that language features are 
added on an experimental basis.  When a language feature (new syntax or 
semantics) goes in to the language, it is there for a long, long time.

If new features are added first to __experimental__ and then to 
__future__ or the non-__experimental__ stdlib namespace, then I just 
have to update all my code to keep using it.  So I'm guaranteed extra 
work whether the feature is successful and is adopted or if it fails and 
is later removed.  I'd rather not have to do the extra work in the 
success case, at least, which is what the existing add-it-and-then-maybe 
-(but-probably-not-)deprecate it approach gives me.

Jean-Paul
>_______________________________________________
>Python-Dev mailing list
>Python-Dev at python.org
>http://mail.python.org/mailman/listinfo/python-dev
>Unsubscribe: http://mail.python.org/mailman/options/python- 
>dev/exarkun%40twistedmatrix.com