Unable to run psql on 9.5 after broken 12 remove

I have a production server running pg9.5 seamlessly.
Yesterday I decided to install libpq to have some crypto functions. 
Unexpectedly, it installed postgresql 12 and its libpq.
I don't need pg 12, so I decided to remove it.
It did not went well

root@datastore-1:/home/user# apt-get --purge remove postgresql-client-12
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following package was automatically installed and is no longer required:
   libuuid-perl
Use 'apt-get autoremove' to remove it.
The following packages will be REMOVED:
   postgresql-12* postgresql-client-12* postgresql-contrib*
0 upgraded, 0 newly installed, 3 to remove and 89 not upgraded.
1 not fully installed or removed.
After this operation, 30.9 MB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 32065 files and directories currently installed.)
Removing postgresql-contrib (12+215.pgdg80+1) ...
Removing postgresql-12 (12.3-1.pgdg80+1) ...
update-alternatives: using 
/usr/share/postgresql/9.5/man/man1/postmaster.1.gz to provide 
/usr/share/man/man1/postmaster.1.gz (postmaster.1.gz) in auto mode
Purging configuration files for postgresql-12 (12.3-1.pgdg80+1) ...
Removing postgresql-client-12 (12.3-1.pgdg80+1) ...
update-alternatives: using /usr/share/postgresql/9.5/man/man1/psql.1.gz 
to provide /usr/share/man/man1/psql.1.gz (psql.1.gz) in auto mode
Processing triggers for postgresql-common (215.pgdg80+1) ...
Building PostgreSQL dictionaries from installed myspell/hunspell packages...
Removing obsolete dictionary files:
Setting up python3.4 (3.4.2-1+deb8u3) ...
   File "/usr/lib/python3.4/http/client.py", line 1014
     raise InvalidURL(f"URL can't contain control characters. {url!r} "
^
SyntaxError: invalid syntax
dpkg: error processing package python3.4 (--configure):
  subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
  python3.4
E: Sub-process /usr/bin/dpkg returned an error code (1)

After this, the package is not anymore on the installed list and I'm not 
able to issue the psql command:

root@datastore-1:/home/user# sudo -u postgres psql
Error: PostgreSQL version 12 is not installed

How can I repair this?
Thanks in advance
Moreno.