String concatenation in Jinja

You can use + if you know all the values are strings. Jinja also provides the ~ operator, which will ensure all values are converted to string first.

{% set my_string = my_string ~ stuff ~ ', '%}

If stuffs is a list of strings, just this would work:

{{ stuffs|join(", ") }}

See join filter documentation, as well as filters in general documentation.

p.s.

More reader friendly way

{{ my ~ ', ' ~ string }}