Bug#878282: hplip: uninstallable in unstable (Depends on python3 < 3.6 but 3.6.3-1 is going to be installed)

[Michael Musenbrock <redeamer@gmx.net>]

Package: hplip
Version: 3.17.9+repack0-1
Severity: serious
Justification: Policy 3.5

The package hplip is not installable in unstable. Or if already installed,
the python3 dependency-package is not upgradable to 3.6.

$ apt-cache show hplip | grep Depends | tr "," "\n"  | grep "python3 "
 python3 (<< 3.6)
 python3 (>= 3.5~)

$ apt-cache policy python3
python3:
  Installed: 3.5.3-3
  Candidate: 3.6.3-1
  Version table:
     3.6.3-1 504
        504 http://ftp.debian.org/debian unstable/main amd64 Packages
 *** 3.5.3-3 503
        503 http://ftp.debian.org/debian testing/main amd64 Packages
        100 /var/lib/dpkg/status

regards Michael

-- Package-specific info:

-- System Information:
Debian Release: buster/sid
  APT prefers unstable
  APT policy: (504, 'unstable'), (503, 'testing'), (502, 'experimental'), (500, 'unstable-debug'), (500, 'testing-debug'), (1, 'experimental-debug')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.13.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=de_AT.UTF-8, LC_CTYPE=de_AT.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages hplip depends on:
ii  adduser                3.116
ii  coreutils              8.28-1
ii  cups                   2.2.4-8
ii  hplip-data             3.17.9+repack0-1
ii  libc6                  2.24-17
ii  libcups2               2.2.4-8
ii  libdbus-1-3            1.11.20-1
ii  libhpmud0              3.17.9+repack0-1
ii  libsane                1.0.25-4.1
ii  libsane-hpaio          3.17.9+repack0-1
ii  libsnmp30              5.7.3+dfsg-1.7+b2
ii  libusb-1.0-0           2:1.0.21-2
ii  lsb-base               9.20170808
ii  policykit-1            0.105-18
ii  printer-driver-hpcups  3.17.9+repack0-1
ii  python3                3.5.3-3
ii  python3-dbus           1.2.4-1+b2
ii  python3-gi             3.24.1-3
ii  python3-pexpect        4.2.1-1
ii  python3-pil            4.2.1-1
ii  python3-reportlab      3.4.0-3
ii  wget                   1.19.1-4
ii  xz-utils               5.2.2-1.3

Versions of packages hplip recommends:
ii  avahi-daemon                  0.7-3
ii  printer-driver-postscript-hp  3.17.9+repack0-1
ii  sane-utils                    1.0.25-4.1

Versions of packages hplip suggests:
pn  hplip-doc              <none>
pn  hplip-gui              <none>
pn  python3-notify2        <none>
pn  system-config-printer  <none>

-- no debconf information