这不是在文档中，但可以使用（预先对猴子补丁有一个基本的了解），在你的models.py或init add：

  from django.contrib.auth.models import Group 

 Group.add_to_class（' foo'，bar）
 

其中bar可以是任何python对象（或方法），例如

  def bar（self）：
 return self.attr * 2 
 pre> 

或使用字段映射：
  Group.add_to_class 'foo'，models.RegexField（r'^ hello $'））
 
 
How add a new field in Group Model of the Django?
To use something like
from django.contrib.auth.models import Group
g = Group.objects.get(pk=1)
g.extra_field = "something"
g.save()
it's posssible? 

EDIT:

I need a persistent extra field.
This isn't in the documentation but fine to use (pre to have a basic understanding of monkey patching), in your models.py or init add:
from django.contrib.auth.models import Group

Group.add_to_class('foo', bar)
Where bar can be any python object (or method), e.g.
def bar(self):
    return self.attr * 2
or using a field mapping:
Group.add_to_class('foo', models.RegexField(r'^hello$'))