returns E:Not locked before setting up the installed package

I suggest you report a bug. Cosmic is not ready and not stable.

If you want an OS that works then I suggest you wipe the install off and do a clean install of Bionic. Bionic is LTS and supported until April 2023.

If you want to report bugs and happy to stomach bugs and feature holes until (and even a little after) release then use Cosmic but don't expect a smooth ride. It's not for casual users (yet)

I'm not using cosmic.
I'm one of the ubuntu-make maintainers.
What I'm trying to do is fix any bugs with cosmic before it's released.

On Fri, 21 Sep 2018, 10:44 actionparsnip, <
<email address hidden>> wrote:

> Your question #674251 on python-apt in Ubuntu changed:
> https://answers.launchpad.net/ubuntu/+source/python-apt/+question/674251
>
> Status: Open => Answered
>
> actionparsnip proposed the following answer:
> I suggest you report a bug. Cosmic is not ready and not stable.
>
> If you want an OS that works then I suggest you wipe the install off and
> do a clean install of Bionic. Bionic is LTS and supported until April
> 2023.
>
> If you want to report bugs and happy to stomach bugs and feature holes
> until (and even a little after) release then use Cosmic but don't expect
> a smooth ride. It's not for casual users (yet)
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
>
> https://answers.launchpad.net/ubuntu/+source/python-apt/+question/674251/+confirm?answer_id=0
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/ubuntu/+source/python-apt/+question/674251
>
> You received this question notification because you asked the question.
>

For me it looks as if the message "E:Not locked" is not part of the apt output (because that follows the text "Subprocess output:"), but of one of the commands before.

Do you have any chance to identify which script and which command could be responsible for that output?

It's the error reported by the python futures thread with the apt commit.
Also, to get this message on cosmic I had to install apt-utils.
In the launchpad build the error was different:

2018-09-19 18:31:09,072 [umake.network.requirements_handler] ERROR: E:Not locked
Subprocess output: debconf: DbDriver "passwords" warning: could not open /var/cache/debconf/passwords.dat: Permission denied
debconf: delaying package configuration, since apt-utils is not installed
dpkg: warning: files list file for package 'testpackage' missing; assuming package has no files currently installed
(Reading database ... 0 files and directories currently installed.)
Preparing to unpack ..././testpackage_0.0.1_all.deb ...
Unpacking testpackage (0.0.1) over (0.0.0) ...
Setting up testpackage (0.0.1) ...

The code in question is:
https://github.com/ubuntu/ubuntu-make/blob/master/umake/network/requirements_handler.py#L207

On 21/09/2018 14:12, Manfred Hampl wrote:
> Your question #674251 on python-apt in Ubuntu changed:
> https://answers.launchpad.net/ubuntu/+source/python-apt/+question/674251
>
> Status: Open => Needs information
>
> Manfred Hampl requested more information:
> For me it looks as if the message "E:Not locked" is not part of the apt
> output (because that follows the text "Subprocess output:"), but of one
> of the commands before.
>
> Do you have any chance to identify which script and which command could
> be responsible for that output?
>

Sorry, but I cannot help further. This goes beyond by knowledge of apt (and python).

The only remark I can do: The python-apt change log shows:

python-apt (1.7.0~alpha2ubuntu3) cosmic; urgency=medium
...
  * Introduce frontend locking
  * Convert apt.Cache.commit and apt_pkg.DepCache.commit to FE lock

So apparently there was a change in lock handling. Maybe the emergence of the "E:Not Locked" message is related to that.

What is a frontend lock exactly?
Am I supposed to lock/unlock the cache if I use python-apt?

Maybe you should try contacting someone of the APT Development Team https://launchpad.net/~deity