How do you parse and inject additional nodes in a Jinja extension?

Question

I am attempting to adapt the Jinja2 WithExtension to produce a generic extension for wrapping a block (followed by some more complex ones).

My objective is to support the following in templates:

{% wrap template='wrapper.html.j2' ... %}
    <img src="{{ url('image:thumbnail' ... }}">
{% endwrap %}

And for wrapper.html.j2 to look like something like:

<div>
    some ifs and stuff
    {{ content }}
    more ifs and stuff
</div>

I believe my example is most of the way there, WithExtension appears to parse the block and then append the AST representation of some {% assign .. %} nodes into the context of the nodes it is parsing.

So I figured I want the same thing, those assignments, followed by an include block, which I'd expect to be able to access those variables when the AST is parsed, and to pass through the block that was wrapped as a variable content.

I have the following thus far:

class WrapExtension(Extension):
    tags = set(['wrap'])

    def parse(self, parser):
        node = nodes.Scope(lineno=next(parser.stream).lineno)
        assignments = []
        while parser.stream.current.type != 'block_end':
            lineno = parser.stream.current.lineno
            if assignments:
                parser.stream.expect('comma')
            target = parser.parse_assign_target()
            parser.stream.expect('assign')
            expr = parser.parse_expression()
            assignments.append(nodes.Assign(target, expr, lineno=lineno))
        content = parser.parse_statements(('name:endwrap',), drop_needle=True)
        assignments.append(nodes.Name('content', content))
        assignments.append(nodes.Include(nodes.Template('wrapper.html.j2'), True, False))
        node.body = assignments
        return node

However, it falls over at my nodes.Include line, I simply get assert frame is None, 'no root frame allowed'. I believe I need to pass AST to nodes.Template rather than a template name, but I don't really know how to parse in additional nodes for the objective of getting AST rather than string output (i.e. renderings) – nor whether this is the right approach. Am I on the right lines, any ideas on how I should go about this?

Can you please add more details on your required result? Do you mean to end up with markup that is contained by the content of `wrapper.html.j2` ? Can you give a content example for `wrapper.html.j2` ? — tutuDajuju, Dec 07 '15 at 13:11
Oh, whoops, in simplifying my example I made it non-sensical, I'll update the examples — Steve, Dec 08 '15 at 09:27

score 7 · Accepted Answer · edited Dec 14 '15 at 17:01

templatetags/wrap.py

class WrapExtension(jinja2.ext.Extension):
    tags = set(['wrap'])
    template = None

    def parse(self, parser):
        tag = parser.stream.current.value
        lineno = parser.stream.next().lineno
        args, kwargs = self.parse_args(parser)
        body = parser.parse_statements(['name:end{}'.format(tag)], drop_needle=True)

        return nodes.CallBlock(self.call_method('wrap', args, kwargs), [], [], body).set_lineno(lineno)

    def parse_args(self, parser):
        args = []
        kwargs = []
        require_comma = False

        while parser.stream.current.type != 'block_end':
            if require_comma:
                parser.stream.expect('comma')

            if parser.stream.current.type == 'name' and parser.stream.look().type == 'assign':
                key = parser.stream.current.value
                parser.stream.skip(2)
                value = parser.parse_expression()
                kwargs.append(nodes.Keyword(key, value, lineno=value.lineno))
            else:
                if kwargs:
                    parser.fail('Invalid argument syntax for WrapExtension tag',
                                parser.stream.current.lineno)
                args.append(parser.parse_expression())

            require_comma = True

        return args, kwargs

    @jinja2.contextfunction
    def wrap(self, context, caller, template=None, *args, **kwargs):
        return self.environment.get_template(template or self.template).render(dict(context, content=caller(), **kwargs))

base.html.j2

<h1>dsd</h1>
{% wrap template='wrapper.html.j2' %}
    {% for i in range(3) %}
        im wrapped content {{ i }}<br>
    {% endfor %}
{% endwrap %}

wrapper.html.j2

Hello im wrapper
<br>
<hr>
{{ content|safe }}
<hr>

args/kwargs parsing get from here https://github.com/Suor/django-cacheops/blob/master/cacheops/jinja2.py

Additionally, the above can be extended to support additional tags with a default template specified as the wrapper:

templatetags/example.py

class ExampleExtension(WrapExtension):
    tags = set(['example'])
    template = 'example.html.j2'

base.html.j2

{% example otherstuff=True, somethingelse=False %}
    {% for i in range(3) %}
        im wrapped content {{ i }}<br>
    {% endfor %}
{% endexample %}

I oversimplified my example a little, I do need any kwargs in addition to `template` passed through to hello_wrapper.js – otherwise this looks good :D — Steve, Dec 09 '15 at 17:30
I am not sure I follow, how do args and kwargs get passed into `CallBlock` in `parse`? I would assume they need to end up being passed to the `render` call in `_wrap`? — Steve, Dec 11 '15 at 11:39
Render called internally. Parse compiles text into nodes. After parsing, renderer call nodes (you can see CallBlock inherits Node class). So, you need prepare CallBlack : set method, args and kwargs converting them into Literal types. — vadimchin, Dec 12 '15 at 10:08
I've updated the example you provided to include passing through args and kwargs, as well as merging those into the context so I can continue to use the request and contextprocessor generated variables within the wrapped template. Additionally, I've chucked in an example of how I use this in other custom tags which have a predefined template. Thanks! — Steve, Dec 14 '15 at 16:46
Sorry to ask a follow-up 3 years later...but in Jinja2 2.10 this is giving `TypeError: object of type 'ExtensionRegistry' has no len()` — Paul Everitt, Sep 20 '18 at 11:36

score 0 · Answer 2 · answered May 29 '16 at 07:03

The better way to handle this is using macros. Define it with:

{% macro wrapper() -%}
<div>
    some ifs and stuff
    {{ caller() }}
    more ifs and stuff
</div>
{%- endmacro %}

And use later with a call tag:

{% call wrapper() %}
    <img src="{{ url('image:thumbnail' ... }}">
{% endcall %}

Macro can have arguments like python function and could be imported:

{% from macros import wrapper %}

See documentation for macro, call and import tags for more details.

How do you parse and inject additional nodes in a Jinja extension?

2 Answers2