Found a solution by using the group argument of the read() function :
#!/usr/bin/python
# -*- coding: utf-8 -*-
import OpenOPC
client = OpenOPC.client()
client.connect('CODESYS.OPC.DA')
tags = client.list("PLC2.Application.GVL.*")
while True:
res = client.read(tags, group='MyGroup')
client.close()