Allow loop on dict keys like python

[guoqiao]

SUMMARY

Allow loop on dict keys like python.

ISSUE TYPE

• Feature Idea

COMPONENT NAME

• task_executor
• loop

ADDITIONAL INFORMATION

Currently ansible support dict loop with dict2items filter:

- name: dict loop example
  debug:
    msg: "my key is {{item.key}}, my value is {{item.value}}"
  loop: '{{my_dict|dict2items}}'

To loop dict, users need to remember a few things in mind:

• filter dict2items
• use item to refer to item
• use item.key to refer to key
• use item.value to refer to value

Considering dict is so common everywhere, above syntax is actually too trivial and overloaded.
The python equavelant is:

for item in [{'key': key, 'value': value} for key, value in my_dict.items()]:
    print(item)

In python, you can also loop dict just like list:

for key in my_dict:
    val = my_dict[key]
    print(val)

this is handy for usage, breif and consistent in syntax.
Any one with basic python expericence will expect to use similar syntax in ansible:

- name: loop dict on key
  debug:
    msg: "dict value for {{item}} is {{my_dict[item]}}"
  loop: '{{my_dict}}'

But ansible loop forbid that, which is a pity and unnecessary.
This patch enables this feature with tiny change.

Example and compare:

- hosts: localhost
  vars:
    my_list:
      - item0
      - item1
    my_dict:
      key0: val0
      key1: val1
  tasks:

    - name: loop on list
      debug: var=item
      loop: '{{my_list}}'

    - name: loop dict on key
      debug:
        msg: "dict value for {{item}} is {{my_dict[item]}}"
      loop: '{{my_dict}}'

    - name: loop dict with dict2items
      debug:
        msg: "dict value for {{item.key}} is {{item.value}}"
      loop: '{{my_dict|dict2items}}'

[ansibot]

Files identified in the description:
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[guoqiao]

I've created a PR #53042 for this.

[ansibot]

Files identified in the description:

• lib/ansible/executor/task_executor.py

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[bcoca]

We prefer to keep the types accepted strict, you can already do what you want this way:

    - name: loop dict on key
      debug:
        msg: "dict value for {{item}} is {{my_dict[item]}}"
      loop: '{{my_dict|list}}'
      vars:
        my_dict:
            a: 1
            b: 2

[guoqiao]

@bcoca nice, this is already much better than dict2items.
However, I am still not comfortable with the fact that loop only works on list, it should work on any iterable/loopable like python.
To be strict on types is good, but for the loop case, it should mean items must be iterable other than items must be list.

[bcoca]

Most non programmers understand 'a list' but not 'iterable', a string is also 'iterable' but we don't want to:

- debug: var=item
 loop: thisisastring

to output

t
h
i
s
....

[sivel]

We have discussed this and decided that loop should not be expanded this way. We have plans to address loop UX, and are exploring several proposals. Please see the following links for more information.

ansible/proposals#99
ansible/proposals#140

If you have further questions please stop by IRC or the mailing list:

• IRC: #ansible on irc.freenode.net
• mailing list: https://groups.google.com/forum/#!forum/ansible-project

[guoqiao]

@sivel thanks.