<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def feincms_breadcrumbs(page, include_self=True):
 """ Generate a list of the page's ancestors suitable for use as breadcrumb navigation. By default, generates an unordered list with the id "breadcrumbs" - override breadcrumbs.html to change this. :: {% feincms_breadcrumbs feincms_page %} """


    if not page or not isinstance(page, Page):
        raise ValueError("feincms_breadcrumbs must be called with a valid Page object")

    ancs = page.get_ancestors()

    bc = [(anc.get_absolute_url(), anc.short_title()) for anc in ancs]

    if include_self:
        bc.append((None, page.short_title()))

    return {"trail": bc}