Task.py

class Task:
    def __init__(self, title, depencies):
        self.title = title
        self.__depencies = depencies

    def execute(self):
        plan = []
        if self.__depencies:
            plan += self.__depencies
            for dep in self.__depencies:
                # if dep.execute():
                #     try:
                #         index = plan.index(dep.execute()[0])
                #     except ValueError:
                #         index = len(plan) - 1
                #         for x in dep.execute():
                #             plan.insert(index, x)
                #         # plan.insert(index, )
                # plan =  + plan
                plan = dep.execute() + plan
        # print('Call execute in {}, returned = {}'.format(self.title, [x.title for x in plan]))
        return plan

    def depencies(self):
        return self.__depencies

    def __str__(self):
        return self.title

# Одинаковые задачи
born = Task('born', [])
school = Task('school', [born])
graduate = Task('graduate', [school])
get_friends = Task('get_friends', [born, school])
get_cash = Task('get_cash', [school, graduate, get_friends])
buy = Task('buy', [school, graduate, get_cash])
getup = Task('getup', [])
cook = Task('cook', [buy, getup])
print('{} → {}'.format([x.title for x in cook.execute()],cook.title))