Django template tag filter for phone display

phone.py

# -*- coding: utf-8 -*-

from django import template

register = template.Library()


@register.filter()
def phone(value):
    return '+%s %s %s %s %s' % (value[0],
                                  value[1:4],
                                  value[4:7],
                                  value[7:9],
                                  value[9:])

try and catch would help if value index is not provided correctly