[MM3-users] How to count the number of members in a list using Mailman client?

I tried to do so using Mailman client but it is really slow for lists with size > 1000. I use the following code snippet:

my_list = client.get_list(listname)

print ("number of members =", len(my_list.members))

Are there any other ways to do so in a much faster speed? Thanks.