[Fixed]-Function in models.py into admin, so I can control

When using moidel methods, you need to add them to the readonly_fields list as well.

class PostAdmin(admin.ModelAdmin):
    fields = ['vote_count']
    readonly_fields = ['vote_count']
    class Meta:
        model = Post

https://docs.djangoproject.com/en/1.9/ref/contrib/admin/#django.contrib.admin.ModelAdmin.readonly_fields