Ansible - how to split a list into two lists? - list

Question

I searched and tried every way to split a list into two lists.
There were no conventional filters or anything supported.
There were examples and posts about combining lists into one, but not the other way around.
I developed below code but it does not work with very strange reason, list does not have attribute 0?
---
- hosts: localhost
gather_facts: no
vars:
- listA: ['a','b','c','d']
- listB: []
- listC: []
tasks:
- block:
- debug:
var: listA[0]
- debug:
var: listB
- debug:
var: listC
- set_fact:
listB: "{{ listB + [listA[item]] }}"
with_sequence: start=0 end=3 stride=2
- set_fact:
listC: "{{ listC + [listA[item]] }}"
with_sequence: start=1 end=3 stride=2
- block:
- debug:
var: listA
- debug:
var: listB
- debug:
var: listC
This is the test run outcome with Ansible 2.1.1.0
$ ansible-playbook test_sequenceeasy.yml
[WARNING]: log file at '{{planfile | dirname}}/AnsibleLog.txt' is not writeable and we cannot create it, aborting
PLAY [localhost] ***************************************************************
TASK [debug] *******************************************************************
ok: [localhost] => {
"listA[0]": "a"
}
TASK [debug] *******************************************************************
ok: [localhost] => {
"listB": []
}
TASK [debug] *******************************************************************
ok: [localhost] => {
"listC": []
}
TASK [set_fact] ****************************************************************
fatal: [localhost]: FAILED! => {"failed": true, "msg": "the field 'args' has an invalid value, which appears to include a variable that is undefined. The error was: 'list object' has no attribute u'0'\n\nThe error appears to have been in '/apps/infra/Tools/Ansible_WLNMiddleware/test_sequenceeasy.yml': line 17, column 5, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n var: listC\n - set_fact:\n ^ here\n"}
NO MORE HOSTS LEFT *************************************************************
[WARNING]: Could not create retry file 'test_sequenceeasy.retry'. [Errno 2] No such file or directory: ''

Answer 1

I found the cause.
The problem about the error message "'list object' has no attribute u'0'" was that Ansible is not recognizing 0 as number, but it think 0 is string.
What? How can Ansible iterate start, end and stride and store the value into "String"? - That I don't know.
But the problem solved with below code update:
---
- hosts: localhost
gather_facts: no
vars:
- listA: ['a','b','c','d']
- listB: []
- listC: []
tasks:
- block:
- debug:
var: listA[0]
- debug:
var: listB
- debug:
var: listC
- set_fact:
listB: "{{ listB + [ listA[item|int] ] }}"
with_sequence: start=0 end=3 stride=2
- set_fact:
listC: "{{ listC + [ listA[item|int] ] }}"
with_sequence: start=1 end=3 stride=2
- block:
- debug:
var: listA
- debug:
var: listB
- debug:
var: listC
And the result is:
$ ansible-playbook test_sequenceeasy.yml
[WARNING]: log file at '{{planfile | dirname}}/AnsibleLog.txt' is not writeable and we cannot create it, aborting
PLAY [localhost] ***************************************************************
TASK [debug] *******************************************************************
ok: [localhost] => {
"listA[0]": "a"
}
TASK [debug] *******************************************************************
ok: [localhost] => {
"listB": []
}
TASK [debug] *******************************************************************
ok: [localhost] => {
"listC": []
}
TASK [set_fact] ****************************************************************
ok: [localhost] => (item=0)
ok: [localhost] => (item=2)
TASK [set_fact] ****************************************************************
ok: [localhost] => (item=1)
ok: [localhost] => (item=3)
TASK [debug] *******************************************************************
ok: [localhost] => {
"listA": [
"a",
"b",
"c",
"d"
]
}
TASK [debug] *******************************************************************
ok: [localhost] => {
"listB": [
"a",
"c"
]
}
TASK [debug] *******************************************************************
ok: [localhost] => {
"listC": [
"b",
"d"
]
}
PLAY RECAP *********************************************************************
localhost : ok=8 changed=0 unreachable=0 failed=0