human
Solve the following python programming problem given the following code:
def _topological_sort(self, goal_info_by_goal) : 
    dependees_by_goal = OrderedDict () 
    def add_dependee(goal, dependee = None) : 
        dependees = dependees_by_goal.get (goal) 
        if (dependees is None) : 
            dependees = set () 
            dependees_by_goal [goal] = dependees 
if dependee : 
            dependees.add (dependee) 
for (goal, goal_info) in goal_info_by_goal.items () : 
        add_dependee (goal) 
        for dependency in goal_info.goal_dependencies : 
            add_dependee (dependency, goal) 
satisfied = set () 
    while dependees_by_goal : 
        count = len (dependees_by_goal) 
        for (goal, dependees) in dependees_by_goal.items () : 
            unsatisfied = len ((dependency - satisfied)) 
            if (unsatisfied == 0) : 
                satisfied.add (goal) 
                dependees_by_goal.pop (goal) 
                (yield goal_info_by_goal [goal]) 
                break 
if (len (dependees_by_goal) == count) : 
            for dependees in dependees_by_goal.values () : 
                dependees.difference_update (satisfied) 
raise self.GoalCycleError ('Cycle detected in goal dependencies:
\t{0}'.format ('
\t'.join (('{0} <- {1}'.format (goal, list (dependees)) for (goal, dependees) in dependees_by_goal.items ())))) 

    
    

    Fix the buggy line: unsatisfied = len ((dependency - satisfied))
assistant
#Here is Python code to fix the buggy line: unsatisfied = len ((dependency - satisfied))
.

unsatisfied = len ((dependees - satisfied))