package update-notifier-common 3.168.4 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

> I've been getting this error since installing Python 3.6

Do you mean you've manually overwritten the system python3 installation on your 16.04 install?

> Where do I get this mythical module

$ dpkg -S python3*deb822|grep '\.py'
python3-debian: /usr/lib/python3/dist-packages/deb822.py
python3-debian: /usr/lib/python3/dist-packages/debian/deb822.py
python3-debian: /usr/share/doc/python3-debian/examples/deb822/grep_native_packages.py
$

> and where should it be installed, so I can get my system back to normal?

You need to fix your system so that 'python3' on the path runs the system python3.5.

How did you install python 3.6?

Based off the DpkgHistoryLog.txt things started to go wrong about here:

Start-Date: 2017-03-10 16:03:09
Commandline: apt install python3.6
Requested-By: laurie (1000)
Install: libpython3.6-minimal:amd64 (3.6.0-2~16.04.york0, automatic), libpython3.6-stdlib:amd64 (3.6.0-2~16.04.york0, automatic), python3.6:amd64 (3.6.0-2~16.04.york0), python3.6-minimal:amd64 (3.6.0-2~16.04.york0, automatic)
Error: Sub-process /usr/bin/dpkg returned an error code (1)
End-Date: 2017-03-10 16:03:48

I tried installing that york0 version of Python 3.6 first, but when it didn't work, I removed it and reinstalled from https://launchpad.net/~fkrull/+archive/ubuntu/deadsnakes.

Judging from the DpkgHistoryLog.txt, it seems like that york0 release messed things up.

How do I go about fixing the system so that the 'python3' on the path points to the system Python 3.5? Is it a symlink that needs changing, or more to it than that? Also, if I do that, will I still be able to use Python 3.6?

I was just checking into where the symlinks are pointing, and at least according to what I see in `/usr/bin/` the symlink for `python` is pointing to Python 2.7, and the one for `python3` is pointing to Python 3.5. But this doesn't make sense, as when I run either of those commands, they both execute Python 3.6.

However, I also found a symlink in `/usr/local/bin` for `python3` and that link is pointing to Python 3.6. There is no symlink in `ust/local/bin` for `python`. Should I remove or change this symlink? If so, how do I go about doing that?

As I said, I tried the `york0` dist first, and removed it, replaced with the Deadsnakes dist which works, but now we have this issue. The `york0` one came from https://blueprints.launchpad.net/~jonathonf/+archive/ubuntu/python-3.6/+sourcepub/7461521/+listing-archive-extra

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