title: Ansible: How to change Python Version
body: <p>Trying to use GNS3 to practice ansible script, there is a docker instance called "Network Automation" with built-in ansible. However, it still uses Python 2.7 as the interpreter: </p>
  
  <pre><code>root@Network-Automation:~# ansible --version
  ansible 2.7.11
    config file = /etc/ansible/ansible.cfg
    configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
    ansible python module location = /usr/lib/python2.7/dist-packages/ansible
    executable location = /usr/bin/ansible
    python version = 2.7.12 (default, Nov 12 2018, 14:36:49) [GCC 5.4.0 20160609]
  </code></pre>
  
  <p>I understand I can use "ansible-playbook --version -e 'ansible_python_interpreter=/usr/bin/python3'" command to run a playbook with Python version 3, or I can specifiy var within the playbook: </p>
  
  <pre><code>- name: Common package
    hosts: all
    gather_facts: no
    vars:
      ansible_python_interpreter: /usr/bin/python3
    roles:
      - { role: python, tags: [ init, python, common, addusers] }
  ...
  ...
  </code></pre>
  
  <p>However, I would like to have a permanent way to force ansible to use Python3 version. How can I achieve this? Thanks. </p>