无法导入名称get_user_model

我使用django-registrations，并在admin.py中添加此代码

   from django.contrib import admin
   from customer.models import Customer
   from .models import UserProfile
   from django.contrib.auth.admin import UserAdmin
   from django.contrib.auth import get_user_model

   class UserProfileInline(admin.StackedInline):
       model = UserProfile
       can_delete = False

   class UserProfileAdmin(UserAdmin):
       inlines=(UserProfileInline, )

   admin.site.unregister(get_user_model())
   admin.site.register(get_user_model(), UserProfileAdmin)
   admin.site.register(Customer)

我收到一个错误：

" cannot import name get_user_model "
in admin.py

我究竟做错了什么？