Display user group in admin interface?

Question

The admin.py at contrib.auth defines the fields to be displayed for the user at the admin interface:

list_display = ('username', 'email', 'first_name', 'last_name', 'is_staff')

I want to see the group of each user here:

Just for testing purpose when you try to add the "group" field it fail:

list_display = ('username', 'email', 'first_name', 'last_name', 'is_staff', 'group')

This error rises: : (admin.E109) The value of 'list_display[5]' must not be a ManyToManyField.

After searching I have found only ways to add an app to the admin interface, or to create a custom user model, but I think I'm missing something.

So, how to do it?

SOLVED --- Thanks to the answer of @{Alexis N-o}

Edit /usr/local/lib/pyton2.7/dist-packages/django/contrib/auth/admin.py

Just before the list_display add this def that seeks for the groups:

def group(self, user):
    groups = []
    for group in user.groups.all():
        groups.append(group.name)
    return ' '.join(groups)
group.short_description = 'Groups'

list_display = ('username', 'email', 'first_name', 'last_name', 'is_staff', 'group')

Then syncdb, and check the change at admin, notice the last column:

Answer 1

It is not possible by default because of the ManyToMany relation but this should work:

def group(self, user):
    groups = []
    for group in user.groups.all():
        groups.append(group.name)
    return ' '.join(groups)
group.short_description = 'Groups'

list_display = ('username', 'email', 'first_name', 'last_name', 'is_staff', 'group')
# The last argument will display a column with the result of the "group" method defined above

You can test it and organize the code to your convenience.