[Twisted-Python] "twistd" in Twisted 16.4.0 can't import modules/packages from current working directory

[Amber "Hawkie" Brown]

> On 4 Jan 2017, at 07:20, Glyph Lefkowitz <glyph at twistedmatrix.com> wrote:
> 
>> 
>> On Jan 2, 2017, at 6:10 AM, Jean-Paul Calderone <exarkun at twistedmatrix.com <mailto:exarkun at twistedmatrix.com>> wrote:
>> 
>> On Thu, Sep 1, 2016 at 11:36 AM, Amber "Hawkie" Brown <hawkowl at atleastfornow.net <mailto:hawkowl at atleastfornow.net>> wrote:
>> 
>> > On 1 Sep 2016, at 21:42, Yuri <yuri_abzyanov at fastmail.fm <mailto:yuri_abzyanov at fastmail.fm>> wrote:
>> >
>> > Hi all
>> >
>> > I couldn't find Twisted-specific group, so posting here.
>> >
>> > Recently Twisted 16.4.0 got released. Yesterday I've tried to upgrade it for my apps and got an error.
>> >
>> > ...
>> >
>> > The errors comes down to this: twistd script does not add current working directory to python path (or removes it, I don't know what exactly happens), so it fails to import any packages/modules from it. The issue does not appear in previous version (Twisted 16.3.2).
>> >
>> > Any ideas what caused it?
>> 
>> Yes -- we moved to using setuptools console scripts, and these console scripts don't add "." to the PYTHONPATH. We realised this in prerelease but decided against fixing it, as it adding the current working dir to the PATH has lead to a lot of  subtle bugs in the past and this is a good chance to make a break from them.
>> 
>> So, in short, this is expected behaviour -- we generally want people to be running twistd, trial, etc on *installed* Python packages -- testing or running from checkouts often hides many bugs about what is or isn't included in the installed package by accident. If you rely on this behaviour, though, set the PYTHONPATH environment variable to "." -- e.g. `env PYTHONPATH=. twistd -n myplugin`.
>> 
>> 
>> FWIW, as a user, it would have been nice to have a NEWS entry for this.  It would have been easier to discover there than searching through the mail archives.
> 
> Yes, there definitely should have been.  We only realized the implications of the change after the fact, and only after some discussion decided that it was in fact desirable and should not be rolled back in a patch release.
> 
> We don't have a process for fixing NEWS files right now, and given that releases are immutable, I wonder if there's any way we could.  So, in the rare case that we mess up this way in the future, what (aside from the mailing list) would be a good communication mechanism to users?
> 
> -glyph

We have, in the past, fixed up historic NEWS files in later releases (e.g. the one which removed 2.6 support). We could always roll these changes into a post1, but, that seems like a lot of effort. Maybe we could put errata on the blog?

- Amber
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