This demonstrates how pallets/jinja#84 breaks certain includes.

Working

mkvirtualenv j26
pip install jinja2==2.6
python gen.py

Output:

<h2>A</h2>
A, A, A
<h2>B</h2>
B, B, B
<h2>C</h2>
C, C, C

Breaking

mkvirtualenv j27
pip install jinja2==2.7
python gen.py

Error:

...
RuntimeError: maximum recursion depth exceeded while calling a Python object