Question

据说循环依赖是坏的和反模式。所以我的问题是下面的代码有什么问题？它是一个循环依赖的例子吗？代码是python伪代码，但应该理解。

class Manager:
    _handlers = []

    def on_config(self):
        # do something...
        # and notify about "event"
        for handler in self._handlers:
            handler()

    def add_change_handler(self, handler):
        self._handlers.append(handler)

    def get_value(self):
        return some_value

class Consumer:
    def __init__(self, manager):
        self._manager = manager
        self._manager.add_change_handler(self._on_event)

    def _on_change(self):
        print('Got event')

    def do_something(self):
        self._manager.get_value()

所以：消费者得到经理：

get_value from it
注册变更事件

反对该解决方案的人的论点是，创建其他类更好，这将是：

了解经理和消费者
收听配置活动
调用使用者的on_change处理程序
消费者只会将经理用于get_value

Answer 1

Circular (or cyclic) imports in Python。这个答案将帮助您更好地了解python中的循环导入。

此代码与循环依赖无关。您也可以将此情况视为商务人士之间的交易。

#!/bin/python
class Businessman:
    _trader_list = []

    def __init__(self, name, goods):
        self.m_name = name
        self.m_goods = goods

    def on_get_goods(self):
        for trader in self._trader_list:
            trader.buy_some(self)

    def add_change_handler(self, handler):
        self._trader_list.append(handler)

    def del_change_handler(self, handler):
        self._trader_list.remove(handler)

    def buy_some(self, from_bussinessman):
        print "{0} will buy some {1}s from {2}".format(
            self.m_name, from_bussinessman.m_goods, from_bussinessman.m_name)

    def get_goods(self):
        print("{0} gets new {1}s.".format(self.m_name, self.m_goods))
        self.on_get_goods()

if __name__ == "__main__":
    bob = Businessman('Bob', 'apple')
    jack = Businessman('Jack', 'banana')
    cream = Businessman('Cream', 'rice')
    # Bob notifys Jack and Cream to buy apples when he gets some.
    seller1 = bob
    seller1.add_change_handler(jack)
    seller1.add_change_handler(cream)
    seller1.get_goods()

结果是

Bob gets new apples.
Jack will buy some apples from Bob
Cream will buy some apples from Bob

这是循环依赖吗？

1 个答案: