filters.py 文件源码

def ifappexists(parser, token):
    """ Conditional Django template tag to check if one or more apps exist.

    Usage: {% ifappexists tag %} ... {% endifappexists %}, or
           {% ifappexists tag inventory %} ... {% else %} ... {% endifappexists %}

    """
    try:
        tokens = token.split_contents()
        apps = []
        apps += tokens[1:]
    except ValueError:
        raise template.TemplateSyntaxError("Tag 'ifappexists' requires at least 1 argument.")

    nodelist_true = parser.parse(('else', 'endifappexists'))
    token = parser.next_token()

    if token.contents == 'else':
        nodelist_false = parser.parse(('endifappexists',))
        parser.delete_first_token()
    else:
        nodelist_false = template.NodeList()

    return AppCheckNode(apps, nodelist_true, nodelist_false)