Bug#1008709: python3-apt: Overriding Package candidate is ignored

[Matt Culler <mculler@tetracore.com>]

Package: python3-apt
Version: 2.2.1
Severity: normal
X-Debbugs-Cc: mculler@tetracore.com

Dear Maintainer,

If I apt remove curl, then run the following code:

>>> import apt
>>> c = apt.Cache()
>>> pkg = c['curl']
>>> pkg.mark_install()
>>> c.commit()
Selecting previously unselected package curl.
(Reading database ... 201874 files and directories currently installed.)
Preparing to unpack .../curl_7.74.0-1.3+deb11u1_amd64.deb ...
Unpacking curl (7.74.0-1.3+deb11u1) ...
Setting up curl (7.74.0-1.3+deb11u1) ...
Processing triggers for man-db (2.9.4-2) ...
True

Curl will be installed.  But then, if I want to install the version from
bullseye-backports:

>>> import apt
>>> c = apt.Cache()
>>> pkg = c['curl']
>>> print(pkg.versions)
[curl=7.82.0-2~bpo11+1, curl=7.74.0-1.3+deb11u1]
>>> pkg.candidate = pkg.versions[0]
>>> pkg.mark_install()
>>> c.commit()
True

The above code does nothing.  However, doing the same thing on a stretch
machine I have access to works, though I used the "whois" package rather
than "curl" because it has a version on stretch-backports.

Thanks,

Matt

-- System Information:
Debian Release: 11.3
  APT prefers stable-security
  APT policy: (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 5.10.0-13-amd64 (SMP w/8 CPU threads)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/bash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages python3-apt depends on:
ii  distro-info-data   0.51+deb11u1
ii  libapt-pkg6.0      2.2.4
ii  libc6              2.31-13+deb11u3
ii  libgcc-s1          10.2.1-6
ii  libstdc++6         10.2.1-6
ii  python-apt-common  2.2.1
ii  python3            3.9.2-3

Versions of packages python3-apt recommends:
ii  iso-codes    4.6.0-1
ii  lsb-release  11.1.0

Versions of packages python3-apt suggests:
ii  apt              2.2.4
pn  python-apt-doc   <none>
pn  python3-apt-dbg  <none>

-- no debconf information