def find_backref_chain(obj, predicate, max_depth=20, extra_ignore=()):
 return _find_chain(obj, predicate, gc.get_referrers, max_depth=max_depth, extra_ignore=extra_ignore)

def find_backref_chain ( obj , predicate , max_depth = 20 , extra_ignore = ( ) ) : return _find_chain ( obj , predicate , gc . get_referrers , max_depth = max_depth , extra_ignore = extra_ignore )
find a shortest chain of references leading to obj .