块分配内的循环？

Question

Here's an elementary loop, which compiles fine when outside of an assignment block:

{% for item in items %}
  <p>{{item}}</p>
{% endfor %}

But when I place the loop inside of an assignment block , like so

{% set stuff %}
  {% for item in items %}
    <p>{{item}}</p>
  {% endfor %}
{% endset %}

I get AssertionError: Tried to resolve a name to a reference that was unknown to the frame ('item') .

The motivation for the question is that I am using macros to avoid code duplication. Eg, I have a number of divs with different fields. One of the divs contains a message to the user. In one (but only one) case, I would like to include a <ul> in this div, and so I would like to loop through the elements in a list, wrapping each of them in <li> tags, before passing the resulting html as an argument to the macro. Hence my question.

Is it possible to use a for loop inside of an assignment block? Or is there a better way of achieving the same thing?

Answer 1

Based on AssertionError: Tried to resolve a name to a reference that was unknown to the frame this problem is only in Jinja2 versions 3.x . Older versions 2.x works correctly.

At this moment it needs to set variable before you use it in block. Maybe later they fix it.

{% set item = None %}

{% set stuff %}
  {% for item in items %}
    <p>{{item}}</p>
  {% endfor %}
{% endset %}

{{ stuff }}

---

But set has one big drawback for me: it can't get arguments and it works only with items .
And it can't works if I set {% set items = other_items %}

I would rather put code in macro to use stuff(main_items) , stuff(other_items) , etc.

{% macro stuff(items) %}
  {% for item in items %}
    <p>{{item}}</p>
  {% endfor %}
{% endmacro %}

{{ stuff(main_items) }}

{{ stuff(other_items) }}

Minimal working code:

from flask import Flask, render_template_string

app = Flask(__name__)

@app.route('/')
def index():
    return render_template_string('''
<h1>SET</h1>

{% set item = None %}

{% set stuff_set %}
  {% for item in items %}
    <p>{{item}}</p>
  {% endfor %}
{% endset %}

{{ stuff_set }}

<h1>MACRO</h1>

{% macro stuff_macro(items) %}
  {% for item in items %}
    <p>{{item}}</p>
  {% endfor %}
{% endmacro %}

{{ stuff_macro(main_items) }}
{{ stuff_macro(other_items) }}
''', items=['A', 'B', 'C'], main_items=[1,2,3], other_items=[4,5,6])

if __name__ == '__main__':
    #app.debug = True 
    app.run()