@register.filter(is_safe=True, needs_autoescape=True)
def join(value, arg, autoescape=None):
    """
    Joins a list with a string, like Python's ``str.join(list)``.
    """
    value = map(force_unicode, value)
    if autoescape:
        value = [conditional_escape(v) for v in value]
    try:
        data = conditional_escape(arg).join(value)
    except __HOLE__: # fail silently but nicely
        return value
    return mark_safe(data)
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.4/django/template/defaultfilters.py/join