1.hosts.j2

# {{ansible_managed}}
127.0.0.1   localhost.localdomain localhost
::1         localhost6.localdomain6 localhost6
{% for item in groups['all'] %}
{% set ip = next(ip for ip in hostvars[item]['ansible_all_ipv4_addresses'] if ip.find("10.") == 0, hostvars[item]['ansible_default_ipv4']) %}
{% if ip %}
{{ ip }} {{ item }}
{% endif %}
{% endfor %}

2.python repl

>>> hostvars = { 'fred': { 'ansible_all_ipv4_addresses': ["10.123.123.123", "184.123.123.123"] } }
>>> item = 'fred'
>>> next((ip for ip in hostvars[item]['ansible_all_ipv4_addresses'] if ip.find("10.") == 0), None)
'10.123.123.123'

3.ansible.err

fatal: [somehost] => {'msg': "file: /some/path/templates/hosts.j2, line number: 5, error: expected token ',', got 'for'", 'failed': True}