human
I wrote the below code

    def expand(r):
        if (r.owner and ((not blockers) or (r not in blockers))):
            return reversed(r.owner.inputs)
    dfs_variables = stack_search(deque(variable_list), expand, 'dfs')
    return dfs_variables

What's a good function header?
assistant
#Here's a good function header.

def ancestors(variable_list, blockers=None):