Wrapping long text sections in Jinja2

Question

I have the definition of a variable, it's name and an associated comment in a YAML file and am trying to use Jinja2 to create an appropriate target file; in this case a proprietary config file

...
- comment: >
      This is a comment which will almost certainly end up longer than standard eighty characters or at least on the occasion on which it does. 
  name: my_useful_variable
  value: /a/long/example/path/to/my/file.txt

I would like this text to be rendered as follows:

# This is a comment which will almost certainly end up
# longer than standard eighty characters or at least on
# the occasion on which it does.
my_useful_variable = "/a/long/example/path/to/my/file.txt"

Does Jinja2 have any way of wrapping text so that the long comment line is limited in length and split over however many lines is necessary?

So far I have:

# {{item.comment}}    
{{item.name}} = "{{item.value}}"

But this of course does not deal with the length of the comment.

Solution

Following on from the answer provided by @blhsing below, I came up with the following macro, which works fine for basic variables and simple lists (i.e. not dictionaries or more complex hierarchical data structures:

{% macro set_params(param_list, ind=4, wid=80) -%}
{% for item in param_list %}
{% if item.comment is defined %}{{item.comment|wordwrap(wid - ind - 2)|replace('',  ' ' * ind +'# ', 1)|replace('\n', '\n' + ' ' * ind + '# ')}}
{% endif %}
{% if item.value is iterable and item.value is not string %}{{item.name|indent(ind, True)}} = [ {% for item_2 in item.value %}{{item_2}}{{ ", " if not loop.last else " " }}{% endfor %}{% else %}{{item.name|indent(ind, True)}} = {{item.value}}{% endif %}
{% endfor %}
{%- endmacro %}

To use this, simply pass a list of items similar to the spec given at the top together with the indentation and the page width.

A bit of explanation:

• Line 3, If comment is defined then it is word wrapped to the correct length bearing in mind the width and the indent. The first replace deals with indenting the first line and the second indents subsequent lines. All prefixed with '# '
• Line 5, depending on whether the variable is simple or iterable, it is rendered in the form name = value or name = [ value1, value2, value3 ]

Of course, it is not fool-proof but it meets my basic requirements.

Answer 1

You can prepend the given string with a newline character, then use the wordwrap filter to wrap the text into multiple lines first, and use the replace filter to replace newline characters with newline plus '# ':

{{ ('\n' ~ item.comment) | wordwrap(78) | replace('\n', '\n# ') }}

The above assumes you want each line to be no more than 80 characters. Change 78 to your desired line width minus 2 to leave room for '# '.