[Python-ideas] Making it easy to prepare for PEP479

[Terry Reedy]

On 5/18/2015 4:14 AM, Ram Rachum wrote:

> I just heard about PEP479, and I want to prepare my open-source projects
> for it.
>
> I have no problem changing the code so it won't depend on StopIteration
> to stop generators, but I'd also like to test it in my test suite. In
> Python 3.5 I could use `from __future__ import generator_stop` so the
> test would be real (i.e. would fail wherever I rely on StopIteration to
> stop a generator). But I can't really put this snippet in my code
> because then it would fail on all Python versions below 3.5.

The purpose of future imports is to allow one to use a future feature, 
at the cost of either not supporting older Python versions, or of 
branching your code and making separate releases.

This future is an anomaly in that it import a future disablement of a 
current feature.  So you just want to make sure your one, no-branch code 
base is ready for that feature removal by not using it now. You do not 
want to have a separate branch and release for 3.5 with the future imports.

Try the following: add the future statement to the top of modules with 
generators, compile with 3.5, and when successful, comment-out the 
statement.  For continued testing, especially with multiple authors, 
write functions to un-comment and re-comment a file.  In the test file:

if <3.5>: uncomment('xyz')  # triggers re-compile on import
import xyz
if <3.5>: recomment('xyz')  # ditto,

If this works, put pep479_helper on pypi.

-- 
Terry Jan Reedy