hp-doctor weird responses based on python version

I get different hp-doctor output if run with python2 vs python3:

On python2, after my workaround at https://bugs.launchpad.net/ubuntu/+source/hplip/+bug/1759278/comments/4:
======================================================================================================
$ python2 `which hp-doctor`
error: cupsext not present in the system. Please re-install HPLIP.
======================================================================================================

(I have had already done sudo apt-get install --reinstall hplip, but installation was mostly pristine anyway)

On python3, however:
======================================================================================================
$ python3 `which hp-doctor`

HP Linux Imaging and Printing System (ver. 3.17.10)
Self Diagnse Utility and Healing Utility ver. 1.0

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

HP Linux Imaging and Printing System (ver. 3.17.10)
Self Diagnse Utility and Healing Utility ver. 1.0

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

Checking for Deprecated items....
error: This distro (i.e linuxmint 19) is either deprecated or not yet supported.
The diagnosis is limited on unsupported platforms. Do you want to continue?(y=yes*, n=no):

Checking for HPLIP updates....
error: Failed to locate hp-upgrade utility

Checking for Dependencies....
warning: 22-19 version is not supported. Using 22-18.2 versions dependencies to verify and install...

---------------
| SYSTEM INFO |
---------------

 Kernel: 4.15.0-29-generic #31-Ubuntu SMP Tue Jul 17 15:39:52 UTC 2018 GNU/Linux
 Host: alkpc-home
 Proc: 4.15.0-29-generic #31-Ubuntu SMP Tue Jul 17 15:39:52 UTC 2018 GNU/Linux
 Distribution: 22 19
 Bitness: 64 bit

-----------------------
| HPLIP CONFIGURATION |
-----------------------

HPLIP-Version: HPLIP 3.17.10
HPLIP-Home: /usr/share/hplip
warning: HPLIP-Installation: Auto installation is not supported for 22 distro 19 version

Current contents of '/etc/hp/hplip.conf' file:
# hplip.conf. Generated from hplip.conf.in by configure.

[hplip]
version=3.17.10

[dirs]
home=/usr/share/hplip
run=/var/run
ppd=/usr/share/ppd/hplip/HP
ppdbase=/usr/share/ppd/hplip
doc=/usr/share/doc/hplip
html=/usr/share/doc/hplip-doc
icon=no
cupsbackend=/usr/lib/cups/backend
cupsfilter=/usr/lib/cups/filter
drv=/usr/share/cups/drv
bin=/usr/bin
apparmor=/etc/apparmor.d
# Following values are determined at configure time and cannot be changed.
[configure]
network-build=yes
libusb01-build=no
pp-build=yes
gui-build=yes
scanner-build=yes
fax-build=yes
dbus-build=yes
cups11-build=no
doc-build=yes
shadow-build=no
hpijs-install=yes
foomatic-drv-install=yes
foomatic-ppd-install=yes
foomatic-rip-hplip-install=no
hpcups-install=yes
cups-drv-install=yes
cups-ppd-install=no
internal-tag=3.17.10
restricted-build=no
ui-toolkit=qt5
qt3=no
qt4=no
qt5=yes
policy-kit=yes
lite-build=no
udev_sysfs_rules=no
hpcups-only-build=no
hpijs-only-build=no
apparmor_build=no

Current contents of '/var/lib/hp/hplip.state' file:
Plugins are not installed. Could not access file: No such file or directory

Current contents of '~/.hplip/hplip.conf' file:
[installation]
date_time = 08/14/18 17:56:43
version = 3.17.10

 <Package-name> <Package-Desc> <Required/Optional> <Min-Version> <Installed-Version> <Status> <Comment>

-------------------------
| External Dependencies |
-------------------------

 error: cups CUPS - Common Unix Printing System REQUIRED 1.1 - INCOMPAT 'CUPS may not be installed or not running'
 gs GhostScript - PostScript and PDF language interpreter and previewer REQUIRED 7.05 9.22 OK -
 error: xsane xsane - Graphical scanner frontend for SANE OPTIONAL 0.9 - MISSING 'xsane needs to be installed'
 scanimage scanimage - Shell scanning program OPTIONAL 1.0 1.0.27 OK -
 error: dbus DBus - Message bus system REQUIRED - 1.12.2 MISSING 'DBUS may not be installed or not running'
 policykit PolicyKit - Administrative policy framework OPTIONAL - 0.105 OK -
 network network -wget OPTIONAL - 1.19.4 OK -
 avahi-utils avahi-utils OPTIONAL - 0.7 OK -

------------------------
| General Dependencies |
------------------------

 error: libjpeg libjpeg - JPEG library REQUIRED - - MISSING 'libjpeg needs to be installed'
 error: cups-devel CUPS devel- Common Unix Printing System development files REQUIRED - - MISSING 'cups-devel needs to be installed'
 error: cups-image CUPS image - CUPS image development files REQUIRED - - MISSING 'cups-image needs to be installed'
 libpthread libpthread - POSIX threads library REQUIRED - b'2.27' OK -
 error: libusb libusb - USB library REQUIRED - 1.0 MISSING 'libusb needs to be installed'
 sane SANE - Scanning library REQUIRED - - OK -
 error: sane-devel SANE - Scanning library development files REQUIRED - - MISSING 'sane-devel needs to be installed'
 error: libnetsnmp-devel libnetsnmp-devel - SNMP networking library development files REQUIRED 5.0.9 - MISSING 'libnetsnmp-devel needs to be installed'
 error: libcrypto libcrypto - OpenSSL cryptographic library REQUIRED - 1.1.0 MISSING 'libcrypto needs to be installed'
 python3X Python 2.2 or greater - Python programming language REQUIRED 2.2 3.6.5 OK -
 error: python3-notify2 Python libnotify - Python bindings for the libnotify Desktop notifications OPTIONAL - - MISSING 'python3-notify2 needs to be installed'
 error: python3-pyqt4-dbus PyQt 4 DBus - DBus Support for PyQt4 OPTIONAL 4.0 - MISSING 'python3-pyqt4-dbus needs to be installed'
 error: python3-pyqt4 PyQt 4- Qt interface for Python (for Qt version 4.x) REQUIRED 4.0 - MISSING 'python3-pyqt4 needs to be installed'
 python3-dbus Python DBus - Python bindings for DBus REQUIRED 0.80.0 1.2.6 OK -
 python3-xml Python XML libraries REQUIRED - 2.2.5 OK -
 error: python3-devel Python devel - Python development files REQUIRED 2.2 3.6.5 MISSING 'python3-devel needs to be installed'
 python3-pil PIL - Python Imaging Library (required for commandline scanning with hp-scan) OPTIONAL - 1.1.7 OK -
 python3-reportlab Reportlab - PDF library for Python OPTIONAL 2.0 3.4.0 OK -

--------------
| COMPILEDEP |
--------------

 error: libtool libtool - Library building support services REQUIRED - - MISSING 'libtool needs to be installed'
 error: gcc gcc - GNU Project C and C++ Compiler REQUIRED - 7.3.0 MISSING 'gcc needs to be installed'
 make make - GNU make utility to maintain groups of programs REQUIRED 3.0 4.1 OK -

---------------------
| Python Extentions |
---------------------

 cupsext CUPS-Extension REQUIRED - 3.17.10 OK -
 hpmudext IO-Extension REQUIRED - 3.17.10 OK -

----------------------
| Scan Configuration |
----------------------

'/etc/sane.d/dll.d/hpaio' not found.
 hpaio HPLIP-SANE-Backend REQUIRED - 3.17.10 OK 'hpaio found in /etc/sane.d/dll.conf'
 scanext Scan-SANE-Extension REQUIRED - 3.17.10 OK -

------------------------------
| DISCOVERED SCANNER DEVICES |
------------------------------

No Scanner found.

--------------------------
| DISCOVERED USB DEVICES |
--------------------------

No devices found.

---------------------------------
| INSTALLED CUPS PRINTER QUEUES |
---------------------------------

C1660w-Color-Printer
--------------------
Type: Unknown
Device URI: usb://Dell/C1660w%20Color%20Printer?serial=ZHA000482
PPD: /etc/cups/ppd/C1660w-Color-Printer.ppd
PPD Description: Xerox Phaser 6000B v1.0
Printer status: printer C1660w-Color-Printer is idle. enabled since Τετ 01 Αυγ 2018 12:05:34 πμ EEST
warning: Printer is not HPLIP installed. Printers must use the hp: or hpfax: CUPS backend for HP-Devices.

Dell-C1660w
-----------
Type: Unknown
Device URI: socket://192.168.1.25:9100
PPD: /etc/cups/ppd/Dell-C1660w.ppd
PPD Description: Xerox Phaser 6000B v1.0
Printer Rendering completedl-C1660w is idle. enabled since Τρι 14 Αυγ 2018 04:49:33 μμ EEST
warning: Printer is not HPLIP installed. Printers must use the hp: or hpfax: CUPS backend for HP-Devices.

--------------
| PERMISSION |
--------------

Missing Required Dependencies
-----------------------------
error: 'libcups2' package is missing or 'cups' service is not running.
error: 'libdbus-1-dev' package is missing/incompatible
error: 'libjpeg8-dev' package is missing/incompatible
error: 'libcups2-dev' package is missing or 'cups' service is not running.
error: 'cups-bsd' package is missing or 'cups' service is not running.
error: 'cups-client' package is missing or 'cups' service is not running.
error: 'libcupsimage2-dev' package is missing or 'cups' service is not running.
error: 'libusb-1.0.0-dev' package is missing/incompatible
error: 'libsane-dev' package is missing/incompatible
error: 'libsnmp-dev' package is missing/incompatible
error: 'snmp-mibs-downloader' package is missing/incompatible
error: 'openssl' package is missing/incompatible
error: 'python3-pyqt4' package is missing/incompatible
error: 'python3-dev' package is missing/incompatible
error: 'libtool' package is missing/incompatible
error: 'libtool-bin' package is missing/incompatible
error: 'build-essential' package is missing/incompatible
Missing Optional Dependencies
-----------------------------
error: 'xsane' package is missing/incompatible
error: 'python3-notify2' package is missing/incompatible
error: 'mate-notification-daemon' package is missing/incompatible
error: 'python3-dbus.mainloop.qt' package is missing/incompatible

ENTER SUDO PASSWORD
-------------------
Please enter the sudoer (alkpc)'s password:
Do you want to update repository and Install missing/incompatible packages. (a=install all*, c=custom_install, s=skip):s
Install manually above missing/incompatible packages.

Checking Permissions....

Checking for Configured Queues....
warning: Device C1660w-Color-Printer is not HPLIP installed. Device must use the hp: or hpfax: to function in HPLIP.
warning: C1660w-Color-Printer is not HP Device.
warning: Device Dell-C1660w is not HPLIP installed. Device must use the hp: or hpfax: to function in HPLIP.
warning: Dell-C1660w is not HP Device.

warning: No Queue(s) configured.

Checking for HP Properitery Plugin's....
No plug-in printers are configured.

Diagnose completed...

More information on Troubleshooting,How-To's and Support is available on http://hplipopensource.com/hplip-web/index.html
======================================================================================================

I might be missing (a few) soft dependencies, but I don't think I "actually" miss anything. Feel free to correct me though.

$ lsb_release -a
Distributor ID: LinuxMint
Description: Linux Mint 19 Tara
Release: 19
Codename: tara

$ LANG= apt-cache policy hplip python python3
hplip:
  Installed: 3.17.10+repack0-5
  Candidate: 3.17.10+repack0-5
  Version table:
 *** 3.17.10+repack0-5 500
        500 http://ubuntu.otenet.gr bionic/main amd64 Packages
        100 /var/lib/dpkg/status
python:
  Installed: 2.7.15~rc1-1
  Candidate: 2.7.15~rc1-1
  Version table:
 *** 2.7.15~rc1-1 500
        500 http://ubuntu.otenet.gr bionic/main amd64 Packages
        100 /var/lib/dpkg/status
python3:
  Installed: 3.6.5-3ubuntu1
  Candidate: 3.6.5-3ubuntu1
  Version table:
 *** 3.6.5-3ubuntu1 500
        500 http://ubuntu.otenet.gr bionic-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     3.6.5-3 500
        500 http://ubuntu.otenet.gr bionic/main amd64 Packages