How to count how many clients are in a django channels Group

I would like to know how to count the number of clients in a Django Channels Group in order to restrict the number of connected clients for example.

I tried to look in the code of Group object but I had no success.

Here my code:

import re
import json
from channels import Group
from channels.sessions import channel_session
from login import login


@channel_session
def ws_connect(message):

    print "Connected"


    if Group("guis").count() > 10: # NOT POSSIBLE

        Group("guis").add(message.reply_channel)
        message.reply_channel.send({'accept': True})

    else:
        message.reply_channel.send({'accept': True})