Try something like:
- hosts: all
  remote_user: root
  gather_facts: false
  tasks:
  - name: Check for Python
      raw: test -e /usr/bin/python
      changed_when: false
      failed_when: false
      register: check_python
 - name: Install Python
      raw: yum -y install python
      when: check_python.rc != 0
It basically checks I python is already installed. If it hasn't it will install it. The task, in this case, installs python on CentOs or Ubuntu using yum.