{% if {{myarr|length}} > 1 %}
<!-- printing some html here -->
{% endif %}

from django import template
register = template.Library()

def length_gt(value, arg):
    """Returns a boolean of whether the value is greater than an argument."""
    try:
        return len(value) > int(arg)
    except (ValueError, TypeError):
        return ''
length_gt.is_safe = False
register.filter(length_gt)

{% if myarr|length > 1 %}
<!-- printing some html here -->
{% endif %}