ansible list in dict (need to understand how it works)

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1

Hi everyone,

I try to understand ansible dictionaries and for my need I use lists in a dictionary which makes the code not simple and I am struggling to understand that:

Below there’re part of my playbook and result:

user_list:

  • name: “name1”
    city: “New York”
    phone: “03-45-67”
  • name: “name2”
    city: “London”
    phone: “04-45-67”
  • name: “name3”
    city: “Berlin”
    phone: “05-45-67”

I need to retrieve information like each phone number for each name and I found this solution:

  • name: debugging dict
    debug:
    msg:
  • “type of user_list: {{ user_list | type_debug }}”
  • " this {{ item[‘name’] }} is relation to this phone : {{ item[‘phone’] }}"
    loop: “{{ user_list }}”

and here’s the result:

TASK [ansible_dict_test : debugging dict] *************************************************************************************************

ok: [localhost] => (item={‘name’: ‘name1’, ‘city’: ‘New York’, ‘phone’: ‘03-45-67’}) => {

“msg”: [

“type of user_list: list”,

" this name1 is relation to this phone : 03-45-67"

]

}

ok: [localhost] => (item={‘name’: ‘name2’, ‘city’: ‘London’, ‘phone’: ‘04-45-67’}) => {

“msg”: [

“type of user_list: list”,

" this name2 is relation to this phone : 04-45-67"

]

}

ok: [localhost] => (item={‘name’: ‘name3’, ‘city’: ‘Berlin’, ‘phone’: ‘05-45-67’}) => {

“msg”: [

“type of user_list: list”,

" this name3 is relation to this phone : 05-45-67"

]

}

I’ve some question about that:

  1. type_debug read from user_list and it is a dict then why it give a list as result?

  2. I has understood, user_list ist the key of dict and the rest is the value. In that case why item[‘name’] is like a key?

  3. Is my playbook good or is a better solution?

Thank you in advance for your help because I am really trying to understand in detail how dictionaries work and I need your advice.

Best regards, H

2

1) type_debug read from user_list and it is a dict then why it give a list
as result?

The value of the variable *user_list* is a list (you wouldn't be able
to iterate it if otherwise)

  user_list:
  - city: New York
    name: name1
    phone: 03-45-67
  - city: London
    name: name2
    phone: 04-45-67
  - city: Berlin
    name: name3
    phone: 05-45-67

2) I has understood, user_list ist the key of dict and the rest is the
value. In that case why item['name'] is like a key?

Yes. *user_list* is dictionary (aka hash, or mapping) with one key
*user_list*. The value of this key is the list. Each item of this
list is a dictionary therefore, in iteration, you can use *name* as a
key in the dictionary *item*.

3) Is my playbook good or is a better solution?

The dictionaries can be searched faster compared to the lists

    - set_fact:
        user_dict: "{{ dict(_keys|zip(user_list)) }}"
      vars:
        _keys: "{{ user_list|map(attribute='name')|list }}"

transforms the list to a dictionary

  phone_book:
    name1:
      city: New York
      name: name1
      phone: 03-45-67
    name2:
      city: London
      name: name2
      phone: 04-45-67
    name3:
      city: Berlin
      name: name3
      phone: 05-45-67

Now you can easily search by names. If the names alone are not unique
create the keys as a combination of attributes

    - set_fact:
        phone_book: "{{ dict(_keys|zip(_vals)) }}"
      vars:
        _names: "{{ user_list|map(attribute='name')|list }}"
        _addrs: "{{ user_list|map(attribute='city')|list }}"
        _keys: "{{ _names|zip(_addrs)|map('join', ',')|list }}"
        _vals: "{{ user_list|map(attribute='phone')|list }}"

create keys by joining the name and the city, and values by selecting
the phone only

  phone_book:
    name1,New York: 03-45-67
    name2,London: 04-45-67
    name3,Berlin: 05-45-67

You need the bracket notation to reference such keys

    phone_book['name2,London']: 04-45-67

You'll have to stick with the lists if you are not able to create
unique keys.

3

Thanks a lot for your detailed instructions.
I understand dictionnaires much better now but I still have to practice.
I know we learn by doing but how do we know what tips or functions we need for a specific case. It is not easy to use something that we don’t know about, by example I didn’t know about zip.
So I need to learn the other functions and how to involve them together.

Best regards, H