How can I assert multiple list items and print all those that failed?

I have a list of dictionaries like so:

myvar:
- host: host1
  version: 2
- host: host2
  version: 5
- host: host3
  version: 4

I’m trying to write an assert task that fails when any of the hosts have a version > 3 and I also want the failure message to include all such hosts. E.g.:

The following hosts have a version greater than 3: host2, host3

The last part is key. I want to display all the hosts that failed the check, not just the first one. Thanks.

It would be easier to define an intermediate variable like hosts_with_version_above_threshold because it will be reused for both the validation and the error message. To filter out the hosts with a version above the threshold we can use the selectattr Jinja2 filter, and to show only the hosts in the message - map (see Loops and list comprehensions for details):

---
- name: Validate the version numbers
  hosts: localhost
  connection: local
  gather_facts: false
  vars:
    myvar:
      - host: host1
        version: 2
      - host: host2
        version: 5
      - host: host3
        version: 4
    threshold: 3
    hosts_with_version_above_threshold: "{{ myvar | selectattr('version', 'gt', threshold) }}"
    message: "The following hosts have a version greater than {{ threshold }}:"
  tasks:
    - name: Assert the version numbers
      assert:
        that: hosts_with_version_above_threshold is not defined or not hosts_with_version_above_threshold
        fail_msg: "{{ message }} {{ hosts_with_version_above_threshold | map(attribute='host') | join(', ') }}"