代理模式和责任链模式 11/30 | Python 主题月

写在前面

本文正在参加「Python主题月」，详情查看活动链接

这个月是 Python 活动月，我决定尝试用 Python 来刷这 30 天的每日一题和随机一题。然后如果周末有精力，我想捣鼓捣鼓这个python-patterns

设计模式对我来说更多的是学习而不是我的个人经验总结，所以我很可能理解偏，如果有大佬见到了请及时指出，我之所以选择在掘金来写一些个人的东西是因为这里的文章质量更高，我不希望后来者看到了这些文章被误导。

代理模式

责任链模式

前面在提 3-tier 的时候提到过这里，现在在这里详细介绍我所理解的 MVC。

MVC 将 GUI 中的数据的呈现与它被接受的过程分开。呈现自然是视图这里，被接受是模型那里，分开是控制器所为。下面看代码吧。


from abc import ABC, abstractmethod


class Model(ABC):
    @abstractmethod
    def __iter__(self):
        pass

    @abstractmethod
    def get(self, item):
        """Returns an object with a .items() call method
        that iterates over key,value pairs of its information."""
        pass

    @property
    @abstractmethod
    def item_type(self):
        pass


class ProductModel(Model):
    class Price(float):
        """A polymorphic way to pass a float with a particular
        __str__ functionality."""

        def __str__(self):
            return f"{self:.2f}"

    products = {
        "milk": {"price": Price(1.50), "quantity": 10},
        "eggs": {"price": Price(0.20), "quantity": 100},
        "cheese": {"price": Price(2.00), "quantity": 10},
    }

    item_type = "product"

    def __iter__(self):
        yield from self.products

    def get(self, product):
        try:
            return self.products[product]
        except KeyError as e:
            raise KeyError(str(e) + " not in the model's item list.")


class View(ABC):
    @abstractmethod
    def show_item_list(self, item_type, item_list):
        pass

    @abstractmethod
    def show_item_information(self, item_type, item_name, item_info):
        """Will look for item information by iterating over key,value pairs
        yielded by item_info.items()"""
        pass

    @abstractmethod
    def item_not_found(self, item_type, item_name):
        pass


class ConsoleView(View):
    def show_item_list(self, item_type, item_list):
        print(item_type.upper() + " LIST:")
        for item in item_list:
            print(item)
        print("")

    @staticmethod
    def capitalizer(string):
        return string[0].upper() + string[1:].lower()

    def show_item_information(self, item_type, item_name, item_info):
        print(item_type.upper() + " INFORMATION:")
        printout = "Name: %s" % item_name
        for key, value in item_info.items():
            printout += ", " + self.capitalizer(str(key)) + ": " + str(value)
        printout += "\n"
        print(printout)

    def item_not_found(self, item_type, item_name):
        print(f'That {item_type} "{item_name}" does not exist in the records')


class Controller:
    def __init__(self, model, view):
        self.model = model
        self.view = view

    def show_items(self):
        items = list(self.model)
        item_type = self.model.item_type
        self.view.show_item_list(item_type, items)

    def show_item_information(self, item_name):
        try:
            item_info = self.model.get(item_name)
        except Exception:
            item_type = self.model.item_type
            self.view.item_not_found(item_type, item_name)
        else:
            item_type = self.model.item_type
            self.view.show_item_information(item_type, item_name, item_info)


def main():
    """
    >>> model = ProductModel()
    >>> view = ConsoleView()
    >>> controller = Controller(model, view)
    >>> controller.show_items()
    PRODUCT LIST:
    milk
    eggs
    cheese
    <BLANKLINE>
    >>> controller.show_item_information("cheese")
    PRODUCT INFORMATION:
    Name: cheese, Price: 2.00, Quantity: 10
    <BLANKLINE>
    >>> controller.show_item_information("eggs")
    PRODUCT INFORMATION:
    Name: eggs, Price: 0.20, Quantity: 100
    <BLANKLINE>
    >>> controller.show_item_information("milk")
    PRODUCT INFORMATION:
    Name: milk, Price: 1.50, Quantity: 10
    <BLANKLINE>
    >>> controller.show_item_information("arepas")
    That product "arepas" does not exist in the records
    """


if __name__ == "__main__":
    import doctest

    doctest.testmod()

复制代码