Make the prepopulated slug field as readonly in Django Admin

[Meenakshi]

I want to make the slug field as read_only depending on the other field value like "lock_slug".

Means There will be Two conditions.

1) When value of "lock_slug" is false then the slug field directly prepopulated from the field "title".

    prepopulated_fields = {"slug": ("title",),}

2) When value of "lock_slug" is true then the slug field make as readonly.

    def get_readonly_fields(self, request, obj = None):
        if obj and obj.lock_slug == True:
            return ('slug',) + self.readonly_fields       
        return self.readonly_fields

These two works fine independently, but problematic when used both.

Means when I try to add get_readonly_fields() on edit then it gives error because of prepopulated_fields.These two crashes with each other.

There will be any solution for working both on admin side.

I also refer below links

http://stackoverflow.com/questions/11601148/making-a-field-readonly-in-django-admin

http://stackoverflow.com/questions/4343535/django-admin-make-a-field-read-only-when-modifying-obj-but-required-when-adding

But not working these two at the same time.

Thanks,

Meenakshi