custom_filters.py

# do you need this?
from jinja2 import contextfilter

class FilterModule(object):
    ''' Extra filters '''

    def filters(self):
        return {
            'sort_hosts': self.sort_hosts,
        }

    def sort_hosts(self, hosts_list, hostvars, key):
        hosts_list.sort(key = lambda x: hostvars[x][key])
        return hosts_list

gistfile1.txt

---
- hosts: localhost

  tasks:

  - command: echo {{ item }}
    delegate_to: "{{ item }}"
    with_items: "{{ groups['sorted']|sort_hosts(hostvars, 'idx') }}"

hosts

[sorted]
two ansible_connection=local idx=2
one ansible_connection=local idx=1
three ansible_connection=local idx=3
four ansible_connection=local idx=4

output.txt

Timothys-MacBook-Pro:ansible-test tgerla$ ansible-playbook -i inventory -c local test-ordering.yml

PLAY [localhost] **************************************************************

GATHERING FACTS ***************************************************************
ok: [localhost]

TASK: [command echo {{ item }}] ***********************************************
changed: [localhost] => (item=one)
changed: [localhost] => (item=two)
changed: [localhost] => (item=three)
changed: [localhost] => (item=four)

PLAY RECAP ********************************************************************
localhost                  : ok=2    changed=1    unreachable=0    failed=0