ansible - NOT RECOMMENDED - example of incredibly nasty/unsafe custom filter to provide list comprehension

ansible.cfg

[defaults]
filter_plugins = ./plugins/filter

custom.py

from __future__ import (absolute_import, division, print_function)
__metaclass__ = type

from ansible import errors

def comp(value, declaration, condition=None):
    """
    support list comprehension

    [x for x in y if something]
    """

    # yuck - using eval() - bad!
    if condition:
        result = [eval(declaration) for x in value if eval(condition)]
    else:
        result = [eval(declaration) for x in value]
        
    return result

class FilterModule(object):

    def filters(self):
        return {
            'comp': comp
        }

output

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

TASK [debug] *******************************************************************************************************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": [
        "c",
        "d"
    ]
}

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

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

TASK [debug] *******************************************************************************************************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": [
        "bob"
    ]
}

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

play.yml

---
- hosts: localhost
  gather_facts: False
  connection: local
  vars:
    mylistoflists: [['a', 'b'],['c', 1],['d', 1]]
  tasks:
    - debug:
        msg: "{{ mylistoflists|comp('x[0]', 'x[1] == 1')|list }}"
        
- hosts: localhost
  gather_facts: False
  connection: local
  vars:
    mylistofdicts:
      - { foo: bob, bar: xyz, type: 1 }
      - { foo: fred, bar: xyz, type: 2 }
  tasks:
    - debug:
        msg: "{{ mylistofdicts|comp(declaration, condition) }}"
      vars:
        declaration: "x['foo']"
        condition: "x['type'] == 1"