you can coerce a str to an int using the add filter
{% for item in numItems|add:"0" %}
https://docs.djangoproject.com/en/dev/ref/templates/builtins/#add
to coerce int to str just use slugify
{{ some_int|slugify }}
EDIT: that said, I agree with the others that normally you should do this in the view – use these tricks only when the alternatives are much worse.