Ansible - get list of multiple attributes and do lineinfile - ansible

Question

I've got multiple values under mounts, I want to have all 'mountpoints' of these attributes.
"mounts": {
"/dev/sdb": {
"fstype": "xfs",
"mountpoint": "/my/point1",
"opts": "defaults,_netdev",
"partition": "/dev/sdb1",
"state": "mounted"
},
"/dev/sdc": {
"fstype": "xfs",
"mountpoint": "/my/point2",
"opts": "defaults,_netdev",
"partition": "/dev/sdc1",
"state": "mounted"
},
"/dev/sdd": {
"fstype": "xfs",
"mountpoint": "/my/point3",
"opts": "defaults,_netdev",
"partition": "/dev/sdd1",
"state": "mounted"
How do I register the three mountpoints in memory for later use, so I get:
/my/point1, /my/point2, /my/point3
I want to place the values in /etc/updatedb.conf with lineinfile, so there should be no spacing.
My end result would look like; cat /etc/updatedb.conf
PRUNEPATHS = "/my/point1 /my/point2 /my/point3"
Currently, I use a template to copy pre-defined variables. But this is not dynamic enough.
I'm playing around how to get the right variables, but no success:
- debug: var=mount[all].mountpoints

Answer 1

To get a list:
- debug: msg="{{ mounts.values() | map(attribute='mountpoint') | list }}"
Or a string:
- debug: msg="{{ mounts.values() | map(attribute='mountpoint') | list | join(' ') }}"

Answer 2

EDIT:
You can get the join of the keys from mounts like this:
mounts: {{ mounts.keys()|join(', ') }}
(old answer that is not valid for this question)
as this describes, you can do
---
- hosts: all
tasks:
- set_fact: mounts={{ ansible_mounts | map(attribute='device')|join(',')}}
- debug: var=ansible_mounts
- debug: var=mounts
sample output
ap test.yml -i hosts -l server
PLAY [all] *********************************************************************
TASK [setup] *******************************************************************
ok: [server]
TASK [set_fact] ****************************************************************
ok: [server]
TASK [debug] *******************************************************************
ok: [server] => {
"ansible_mounts": [
{
"device": "/dev/sda1",
"fstype": "ext4",
"mount": "/",
"options": "rw,errors=remount-ro",
"size_available": 2890289152,
"size_total": 9376751616,
"uuid": "N/A"
},
{
"device": "/dev/sdb1",
"fstype": "ext4",
"mount": "/mnt/data1",
"options": "rw",
"size_available": 50684461056,
"size_total": 200674758656,
"uuid": "N/A"
}
]
}
TASK [debug] *******************************************************************
ok: [server] => {
"mounts": "/dev/sda1,/dev/sdb1"
}
PLAY RECAP *********************************************************************
server : ok=4 changed=0 unreachable=0 failed=0