Ansible setting of hostname from inventory, but ignoring IP addresses

hosts.yml

- name: Ensure hostname set
  hostname: name={{ inventory_hostname }}
  when: inventory_hostname is not match('(\d{1,3}\.){3}\d{1,3}')

- name: Ensure hostname is in /etc/hosts
  lineinfile:
    dest=/etc/hosts
    regexp="^{{ ansible_default_ipv4.address }}.+$"
    line="{{ ansible_default_ipv4.address }} {{ ansible_fqdn }} {{ ansible_hostname }}"