how to know which python version is installed ubuntu code example

Example 1: check all python versions ubuntu

# View as version vise:
for p in $(compgen -c python); do printf "%-16s" $p; $p --version; done
python2.7      Python 2.7.6
python3.4m     Python 3.4.3

# view as:
$ compgen -c python
python2.7
python3.4m

Example 2: check python version ubuntu

python3 --version