I had hard times searching for the reason fsCalendar couldn't render.  I found it was because '{{years[0]}}' was interpreted as '[[years[0]]]' as I have '[[' and ']]' as interpolation start and stop symbols respectively (because '{{' and '}}' interfere with jinja2 templating). Adding spaces solved the problem.
Merge pull request #26 from Viruzzz-kun/master

Added spaces inside interpolated expressions