It should be installed by default in any GNU/Linux computer. Of course you can check the version installed:

_$: python --version
Python 2.7.12

_$: python3 --version
Python 3.5.2

You can check all python binaries available in your system:

_$: ls -1 /usr/bin/python*


If you are going to do any development, you almost certainly want to install the python development package:

_$: sudo apt-get install python-dev    # Python 2
_$: sudo apt     install python3-dev   # Python 3 (generic, install either this one or the one for your specific version)
_$: sudo apt     install python3.4-dev # Python 3.4
_$: sudo apt     install python3.5-dev # Python 3.5