I use a rest sensor to retrieve a list but I cannot search in this list. I can if I write this list manually.
Here is the output of my template.
Search in list from state
{% set mystatelist = states.sensor.anniversaires.state %}
{{ mystatelist }}
{{ mystatelist.0 }}
Search in list from variable
{% set myvariablelist = {'event1': 'Anniversaire', 'date': '2021-06-04'},{'event2': 'Anniversaire', 'date': '2021-06-05'},{'event3': 'Anniversaire', 'date': '2021-06-08'}%}
{{ myvariablelist }}
{{ myvariablelist.0 }}
Search in list from state
{'event1': 'Anniversaire', 'date': '2021-06-04'},{'event2': 'Anniversaire', 'date': '2021-06-05'},{'event3': 'Anniversaire', 'date': '2021-06-08'}
{
Search in list from variable
({'event1': 'Anniversaire', 'date': '2021-06-04'}, {'event2': 'Anniversaire', 'date': '2021-06-05'}, {'event3': 'Anniversaire', 'date': '2021-06-08'})
{'event1': 'Anniversaire', 'date': '2021-06-04'}
A list should look like this: ["a", "b", "c"]. None of your examples is a list: the manually-written one has turned into a Python tuple — a bit like a list but in parentheses ("a", "b", "c") and the indexing does work.