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

[Amber "Hawkie" Brown]

> On 1 Sep 2016, at 21:42, Yuri <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`.

- Amber
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