[Twisted-Python] Strange ImportError after switching from OS package to pip

[Glyph Lefkowitz]

> On Jan 17, 2017, at 9:53 AM, Роман Мещеряков <romanmescheryakov at yandex.ru> wrote:
> 
> Hi everyone! The 14.0.2 version of Twisted is latest that is available for Raspbian as a package, so until today I used it. I run my Twisted application in the following way:
> twistd -ny master_player2.tac
> There were no problems with starting my application.
> Yesterday I started facing strange problem with unjellying which looked like a bug. So I decided to remove old package version of Twisted (installed using apt-get) and install latest version using pip (which was 16.6.0). The commands I issued were (typing by memory):
>  
> sudo apt-get purge python-twisted
> sudo apt-get autoremove
> sudo pip install Twisted

I should point out here that you should not modify your operating system like this.  If /usr/ is managed with 'apt', then let it do that; 'pip' and 'apt' can't manage the same files without stomping on each other.  Better would be to create a virtualenv for your application and 'pip install Twisted[tls,http2]' in there.

In this specific case, on a raspberry pi which is purpose-built, you'll probably be fine, but `sudo pip install` is just a bad habit to get into.

> After issuing these commands, without rebooting, I tried running my program as usual:
> ...
> exceptions.ImportError: No module named shared
> Failed to load application: No module named shared

Try `PYTHONPATH=.` on the command line before `twistd`.

(Also, you might want to try `twist` instead, then you don't need the `-n` option...)

-glyph

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