apt / apt-get / aptitude recipes

First, update your package lists

• $ sudo apt-get update

Get all available versions of a package (when you have multiple repos)

• $ apt-cache madison python-panic

you can install one specific version with 


apt-get install <packagename>=<packageversion>

Get currently installed version; probably there's a better way, but a simulated call to apt-get install will print the already installed package

• $ sudo apt-get -s install python-panic

Addendum by SB:

$ apt-cache policy ctpc
ctpc:
  Installed: 2.0.13-0~bpo9+0~alba+1
  Candidate: 2.0.13-0~bpo9+0~alba+1
  Version table:
 *** 2.0.13-0~bpo9+0~alba+1 500

There is also another alternative from apt instead of apt-cache

$ apt list ctpc -a
Listing... Done
ctpc/stretch,now 2.0.13-0~bpo9+0~alba+1 all [installed]
ctpc/stretch 2.0.11-0~bpo9+0~alba+1 all
(...)

Use the one that fits better to your needs.