execution output

[vdo023@localhost selectattr]$ ansible-playbook -i "localhost," ./selectattr-playbook.yml

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

TASK [extract the emails for users without a password] ********************************************************************************************
ok: [localhost]

TASK [debug message] ******************************************************************************************************************************
ok: [localhost] => (item=johnsmith@gmail.com) => {
    "changed": false,
    "item": "johnsmith@gmail.com",
    "msg": "email this user johnsmith@gmail.com and ask them to set a password"
}
ok: [localhost] => (item=janedoe@hotmail.com) => {
    "changed": false,
    "item": "janedoe@hotmail.com",
    "msg": "email this user janedoe@hotmail.com and ask them to set a password"
}

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

selectattr-playbook.yml

---
- hosts: localhost
  gather_facts: False
  connection: local
  vars:
    users:
      - name: john
        email: johnsmith@gmail.com
      - name: jane
        email: janedoe@hotmail.com
      - name: fred
        email: fredbloggs@outlook.com
        password: 123!abc
  tasks:
    - name: extract the emails for users without a password
      set_fact:
        emails: "{{ users | selectattr('password', 'undefined') | map(attribute='email') | list }}"
    - name:  debug message
      debug:
        msg: "email this user {{ item }} and ask them to set a password"
      with_items: "{{ emails }}"