python设计模式

软件工程中，设计模式是指软件设计问题的推荐方案。设计模式一般是描述如何组织代码和 使用最佳实践来解决常见的设计问题。

创建型模式，处理对象创建的设计模式.

工厂模式

工厂通常有两种形式：

第一种是工厂方法（Factory Method），

它是一个方法（Python 术语来说，是一个函数），对不同的输入参数返回不同的对象；

示例中函数connection_factory是一个工厂方法，基于输入文件路径的扩展名返回一个 JSONConnector或XMLConnector的实例

import xml.etree.ElementTree as etree
import json


class JSONConnector:

    def __init__(self, filepath):
        self.data = dict()
        with open(filepath, mode='r', encoding='utf-8') as f:
            self.data = json.load(f)

    @property
    def parsed_data(self):
        return self.data


class XMLConnector:

    def __init__(self, filepath):
        self.tree = etree.parse(filepath)

    @property
    def parsed_data(self):
        return self.tree


def connection_factory(filepath):
    if filepath.endswith('json'):
        connector = JSONConnector
    elif filepath.endswith('xml'):
        connector = XMLConnector
    else:
        raise ValueError('Cannot connect to {}'.format(filepath))
    return connector(filepath)


def connect_to(filepath):
    factory = None
    try:
        factory = connection_factory(filepath)
    except ValueError as ve:
        print(ve)
    return factory


def main():
    sqlite_factory = connect_to('data/person.sq3')
    print()

    xml_factory = connect_to('data/person.xml')
    xml_data = xml_factory.parsed_data
    liars = xml_data.findall(".//{}[{}='{}']".format('person',
                                                     'lastName', 'Liar'))
    print('found: {} persons'.format(len(liars)))
    for liar in liars:
        print('first name: {}'.format(liar.find('firstName').text))
        print('last name: {}'.format(liar.find('lastName').text))
        [print('phone number ({})'.format(p.attrib['type']),
               p.text) for p in liar.find('phoneNumbers')]

    print()

    json_factory = connect_to('data/donut.json')
    json_data = json_factory.parsed_data
    print('found: {} donuts'.format(len(json_data)))
    for donut in json_data:
        print('name: {}'.format(donut['name']))
        print('price: ${}'.format(donut['ppu']))
        [print('topping: {} {}'.format(t['id'], t['type'])) for t in donut['topping']]

if __name__ == '__main__':
    main()

第二种是抽象工厂，

它是一组用于创建一系列相关事物对象的工厂方法。是工厂方法模式的一种泛化，应用需要许多工厂方法，那么将创建一系列对象的过程合并在一起。

示例中main()函数，该函数请求用户的姓名和年龄，并根据用户的年龄决定该玩哪个游戏。

# Author:song
class Frog:

    def __init__(self, name):
        self.name = name

    def __str__(self):
        return self.name

    def interact_with(self, obstacle):
        print('{} the Frog encounters {} and {}!'.format(self,
                                                         obstacle, obstacle.action()))


class Bug:

    def __str__(self):
        return 'a bug'

    def action(self):
        return 'eats it'


class FrogWorld:
        """抽象工厂，其主要职责是创建游戏的主人公和障碍物"""
    def __init__(self, name):
        print(self)
        self.player_name = name

    def __str__(self):
        return '

	------ Frog World ———'

    def make_character(self):
        return Frog(self.player_name)

    def make_obstacle(self):
        return Bug()


class Wizard:

    def __init__(self, name):
        self.name = name

    def __str__(self):
        return self.name

    def interact_with(self, obstacle):
        print('{} the Wizard battles against {} and {}!'.format(self, obstacle, obstacle.action()))


class Ork:

    def __str__(self):
        return 'an evil ork'

    def action(self):
        return 'kills it'


class WizardWorld:
    """抽象工厂，其主要职责是创建游戏的主人公和障碍物"""
    def __init__(self, name):
        print(self)
        self.player_name = name

    def __str__(self):
        return '

	------ Wizard World ———'

    def make_character(self):
        return Wizard(self.player_name)

    def make_obstacle(self):
        return Ork()


class GameEnvironment:

    def __init__(self, factory):
        self.hero = factory.make_character()
        self.obstacle = factory.make_obstacle()

    def play(self):
        self.hero.interact_with(self.obstacle)


def validate_age(name):
    try:
        age = input('Welcome {}. How old are you? '.format(name))
        age = int(age)
    except ValueError as err:
        print("Age {} is invalid, please try 
        again…".format(age))
        return (False, age)
    return (True, age)


def main():
    name = input("Hello. What's your name? ")
    valid_input = False
    while not valid_input:
        valid_input, age = validate_age(name)
    game = FrogWorld if age < 18 else WizardWorld
    environment = GameEnvironment(game(name))
    environment.play()

if __name__ == '__main__':
    main()

建造者设计模式

将一个复杂对象的构造过程与其表现分离，如果我们知道一个对象必须经过多个步骤来创建，并且要求同一个构造过程可以产生不同的表现，就可以使用建造者模式。

# Author:song
# coding: utf-8


class Computer:

    def __init__(self, serial_number):
        self.serial = serial_number
        self.memory = None      # 单位为GB
        self.hdd = None         # 单位为GB
        self.gpu = None

    def __str__(self):
        info = ('Memory: {}GB'.format(self.memory),
                'Hard Disk: {}GB'.format(self.hdd),
                'Graphics Card: {}'.format(self.gpu))
        return '
'.join(info)


class ComputerBuilder:

    def __init__(self):
        self.computer = Computer('AG23385193')

    def configure_memory(self, amount):
        self.computer.memory = amount

    def configure_hdd(self, amount):
        self.computer.hdd = amount

    def configure_gpu(self, gpu_model):
        self.computer.gpu = gpu_model


class HardwareEngineer:

    def __init__(self):
        self.builder = None

    def construct_computer(self, memory, hdd, gpu):
        self.builder = ComputerBuilder()
        [step for step in (self.builder.configure_memory(memory),
                           self.builder.configure_hdd(hdd),
                           self.builder.configure_gpu(gpu))]

    @property
    def computer(self):
        return self.builder.computer


def main():
    engineer = HardwareEngineer()
    engineer.construct_computer(hdd=500, memory=8, gpu='GeForce GTX 650 Ti')
    computer = engineer.computer
    print(computer)

if __name__ == '__main__':
    main()

原型设计模式

无非就是克隆一个对象。原始对象的所有数据都被简单地复制到克隆对象中，用于创建对象的完全副本。示例图书信息版本信息，是深拷贝，旨在创建新对象而不影响原先数据

# Author:song
# coding: utf-8

import copy
from collections import OrderedDict


class Book:

    def __init__(self, name, authors, price, **rest):
        '''rest的例子有：出版商，长度，标签，出版日期'''
        self.name = name
        self.authors = authors
        self.price = price
        self.__dict__.update(rest)

    def __str__(self):
        mylist = []
        ordered = OrderedDict(sorted(self.__dict__.items()))
        for i in ordered.keys():
            mylist.append('{}: {}'.format(i, ordered[i]))
            if i == 'price':
                mylist.append('$')
            mylist.append('
')
        return ''.join(mylist)


class Prototype:

    def __init__(self):
        self.objects = dict()

    def register(self, identifier, obj):
        self.objects[identifier] = obj

    def unregister(self, identifier):
        del self.objects[identifier]

    def clone(self, identifier, **attr):
        found = self.objects.get(identifier)
        if not found:
            raise ValueError('Incorrect object identifier: {}'.format(identifier))
        obj = copy.deepcopy(found)
        obj.__dict__.update(attr)
        return obj


def main():
    b1 = Book('The C Programming Language', ('Brian W. Kernighan', 'Dennis M.Ritchie'), price=118, publisher='Prentice Hall',
              length=228, publication_date='1978-02-22', tags=('C', 'programming', 'algorithms', 'data structures'))

    prototype = Prototype()
    cid = 'k&r-first'
    prototype.register(cid, b1)
    b2 = prototype.clone(cid, name='The C Programming Language(ANSI)', price=48.99,
                         length=274, publication_date='1988-04-01', edition=2)

    for i in (b1, b2):
        print(i)
    print('ID b1 : {} != ID b2 : {}'.format(id(b1), id(b2)))

if __name__ == '__main__':
    main()

结构型模式，介绍处理一个系统中不同实体（类、对象等）之间关系的设计模式，关注的是提供一 种简单的对象组合方式来创造新功能.

适配器模式（Adapter pattern）

是一种结构型设计模式，帮助我们实现两个不兼容接口之间的兼容，无需修改不兼容模型的源代码就能获得接口的 一致性

"""。在Synthesizer类中，主要动作由play()方法执行。在Human类中，主要动作由speak()方法执行，客户端仅知道如何调用execute()方法，并不知道play()和speak()。在不改变Synthesizer和Human类的前提运行代码"""


class Synthesizer:

    def __init__(self, name):
        self.name = name

    def __str__(self):
        return 'the {} synthesizer'.format(self.name)

    def play(self):
        return 'is playing an electronic song'


class Human:

    def __init__(self, name):
        self.name = name

    def __str__(self):
        return '{} the human'.format(self.name)

    def speak(self):
        return 'says hello'



class Computer:
    def __init__(self, name):
        self.name = name

    def __str__(self):
        return 'the {} computer'.format(self.name)

    def execute(self):
        return 'executes a program'


class Adapter:

    def __init__(self, obj, adapted_methods):
        self.obj = obj
        self.__dict__.update(adapted_methods)

    def __str__(self):
        return str(self.obj)


def main():
    objects = [Computer('Asus')]
    synth = Synthesizer('moog')
    objects.append(Adapter(synth, dict(execute=synth.play)))
    human = Human('Bob')
    objects.append(Adapter(human, dict(execute=human.speak)))

    for i in objects:
        print('{} {}'.format(str(i), i.execute()))

if __name__ == "__main__":
    main()

修饰器（Decorator）模式

能够以透明的方式（不会影响其他对象）动态地将功能添加到一个对象中。

# Author:song
# coding: utf-8

import functools


def memoize(fn):
    known = dict()

    @functools.wraps(fn)
    def memoizer(*args):
        if args not in known:
            known[args] = fn(*args)
        return known[args]

    return memoizer


@memoize
def nsum(n):
    '''返回前n个数字的和'''
    assert(n >= 0), 'n must be >= 0'
    return 0 if n == 0 else n + nsum(n-1)


@memoize
def fibonacci(n):
    '''返回斐波那契数列的第n个数'''
    assert(n >= 0), 'n must be >= 0'
    return n if n in (0, 1) else fibonacci(n-1) + fibonacci(n-2)

if __name__ == '__main__':
    from timeit import Timer
    measure = [{'exec': 'fibonacci(100)', 'import': 'fibonacci',
                'func': fibonacci}, {'exec': 'nsum(200)', 'import': 'nsum',
                                     'func': nsum}]
    for m in measure:
        t = Timer('{}'.format(m['exec']), 'from __main__ import 
            {}'.format(m['import']))
        print('name: {}, doc: {}, executing: {}, time: 
            {}'.format(m['func'].__name__, m['func'].__doc__,
                       m['exec'], t.timeit()))

 外观设计模式

有助于隐藏系统的内部复杂性，并通过一个简化的接口向客户端暴露必要的部分，本质上，外观（Facade）是在已有复杂系统之上实现的一个抽象层。这种模式是为复杂系统提供一个简单接口的理想方式

from enum import Enum
from abc import ABCMeta, abstractmethod

State = Enum('State', 'new running sleeping restart zombie')


class User:
    pass


class Process:
    pass


class File:
    pass


class Server(metaclass=ABCMeta):

    @abstractmethod
    def __init__(self):
        pass

    def __str__(self):
        return self.name

    @abstractmethod
    def boot(self):
        pass

    @abstractmethod
    def kill(self, restart=True):
        pass


class FileServer(Server):

    def __init__(self):
        '''初始化文件服务进程要求的操作'''
        self.name = 'FileServer'
        self.state = State.new

    def boot(self):
        print('booting the {}'.format(self))
        '''启动文件服务进程要求的操作'''
        self.state = State.running

    def kill(self, restart=True):
        print('Killing {}'.format(self))
        '''杀死文件服务进程要求的操作'''
        self.state = State.restart if restart else State.zombie

    def create_file(self, user, name, permissions):
        '''检查访问权限的有效性、用户权限，等等'''

        print("trying to create the file '{}' for user '{}' with permissions {}".format(name, user, permissions))


class ProcessServer(Server):

    def __init__(self):
        '''初始化进程服务进程要求的操作'''
        self.name = 'ProcessServer'
        self.state = State.new

    def boot(self):
        print('booting the {}'.format(self))
        '''启动进程服务进程要求的操作'''
        self.state = State.running

    def kill(self, restart=True):
        print('Killing {}'.format(self))
        '''杀死进程服务进程要求的操作'''
        self.state = State.restart if restart else State.zombie

    def create_process(self, user, name):
        '''检查用户权限、生成PID，等等'''

        print("trying to create the process '{}' for user '{}'".format(name, user))


class WindowServer:
    pass


class NetworkServer:
    pass


class OperatingSystem:

    '''外观'''

    def __init__(self):
        self.fs = FileServer()
        self.ps = ProcessServer()

    def start(self):
        [i.boot() for i in (self.fs, self.ps)]

    def create_file(self, user, name, permissions):
        return self.fs.create_file(user, name, permissions)

    def create_process(self, user, name):
        return self.ps.create_process(user, name)


def main():
    os = OperatingSystem()
    os.start()
    os.create_file('foo', 'hello', '-rw-r-r')
    os.create_process('bar', 'ls /tmp')

if __name__ == '__main__':
    main()

享元设计模式

通过为相似对象引入数据共享来最小化内存使用，旨在优化性能和内存使用,一个享元（Flyweight）就是一个包含状态独立的不可变（又称固有的）数据的 共享对象。依赖状态的可变（又称非固有的）数据不应是享元的一部分，因为每个对象的这种信 息都不同，无法共享。

# coding: utf-8

import random
from enum import Enum

TreeType = Enum('TreeType', 'apple_tree cherry_tree peach_tree')


class Tree:
    pool = dict()

    def __new__(cls, tree_type):
        obj = cls.pool.get(tree_type, None)
        if not obj:
            obj = object.__new__(cls)
            cls.pool[tree_type] = obj
            obj.tree_type = tree_type
        return obj

    def render(self, age, x, y):
        print('render a tree of type {} and age {} at ({}, {})'.format(self.tree_type, age, x, y))


def main():
    rnd = random.Random()
    age_min, age_max = 1, 30    # 单位为年
    min_point, max_point = 0, 100
    tree_counter = 0

    for _ in range(10):
        t1 = Tree(TreeType.apple_tree)
        t1.render(rnd.randint(age_min, age_max),
                  rnd.randint(min_point, max_point),
                  rnd.randint(min_point, max_point))
        tree_counter += 1

    for _ in range(3):
        t2 = Tree(TreeType.cherry_tree)
        t2.render(rnd.randint(age_min, age_max),
                  rnd.randint(min_point, max_point),
                  rnd.randint(min_point, max_point))
        tree_counter += 1

    for _ in range(5):
        t3 = Tree(TreeType.peach_tree)
        t3.render(rnd.randint(age_min, age_max),
                  rnd.randint(min_point, max_point),
                  rnd.randint(min_point, max_point))
        tree_counter += 1

    print('trees rendered: {}'.format(tree_counter))
    print('trees actually created: {}'.format(len(Tree.pool)))

    t4 = Tree(TreeType.cherry_tree)
    t5 = Tree(TreeType.cherry_tree)
    t6 = Tree(TreeType.apple_tree)
    print('{} == {}? {}'.format(id(t4), id(t5), id(t4) == id(t5)))
    print('{} == {}? {}'.format(id(t5), id(t6), id(t5) == id(t6)))

if __name__ == '__main__':
    main()

模型—视图—控制器（Model-View-Controller，MVC）模式

模型—视图—控制器（Model-View-Controller，MVC）模式是应用到面向对象编程的Soc原则。 模式的名称来自用来切分软件应用的三个主要部分，即模型部分、视图部分和控制器部分。MVC 被认为是一种架构模式而不是一种设计模式。架构模式与设计模式之间的区别在于前者比后者的范畴更广

# Author:song
quotes = ('A man is not complete until he is married. Then he is finished.',
          'As I said before, I never repeat myself.',
          'Behind a successful man is an exhausted woman.',
          'Black holes really suck...', 'Facts are stubborn things.')


class QuoteModel:
    """模型极为简约，只有一个get_quote()方法，基于索引n从quotes元组中返回对应的名人
名言（字符串）"""

    def get_quote(self, n):
        try:
            value = quotes[n]
        except IndexError as err:
            value = 'Not found!'
        return value


class QuoteTerminalView:
    """视图有三个方法，分别是show()、error()和select_quote()。show()用于在屏幕上输
出一句名人名言（或者输出提示信息Not found!）；error()用于在屏幕上输出一条错误消息；
select_quote()用于读取用户的选择"""

    def show(self, quote):
        print('And the quote is: "{}"'.format(quote))

    def error(self, msg):
        print('Error: {}'.format(msg))

    def select_quote(self):
        return input('Which quote number would you like to see?')


class QuoteTerminalController:
    """控制器负责协调。__init__()方法初始化模型和视图。run()方法校验用户提供的名言索
引，然后从模型中获取名言，并返回给视图展示"""0
    def __init__(self):
        self.model = QuoteModel()
        self.view = QuoteTerminalView()

    def run(self):
        valid_input = False
        while not valid_input:
            n = self.view.select_quote()
            try:
                n = int(n)
            except ValueError as err:
                self.view.error("Incorrect index '{}'".format(n))
            else:
                valid_input = True
        quote = self.model.get_quote(n)
        self.view.show(quote)


def main():
    controller = QuoteTerminalController()
    while True:
        controller.run()

if __name__ == '__main__':
    main()

代理设计模式（Proxy design pattern）

访问某个对象之前执行一个或多个重要的操作。对象在访问实际对象之前执行重要操作而得其名。

使用代理模式实现一个实际类的替代品，这 样可以在访问实际类之前（或之后）做一些额外的事情。四个不同类型

  远程代理，代表一个活跃于远程位置（例如，我们自己的远程服务器或云服务）的对象。

 虚拟代理，将一个对象的初始化延迟到真正需要使用时进行。

 保护/防护代理，用于对处理敏感信息的对象进行访问控制。

 当我们希望通过添加帮助信息（比如，引用计数）来扩展一个对象的行为时，可以使用 智能（引用）代理。

# Author:song
class SensitiveInfo:

    def __init__(self):
        self.users = ['nick', 'tom', 'ben', 'mike']

    def read(self):
        print('There are {} users: {}'.format(len(self.users), ' '.join(self.users)))

    def add(self, user):
        self.users.append(user)
        print('Added user {}'.format(user))


class Info:

    '''SensitiveInfo的保护代理'''

    def __init__(self):
        self.protected = SensitiveInfo()
        self.secret = '0xdeadbeef'

    def read(self):
        self.protected.read()

    def add(self, user):
        sec = input('what is the secret? ')
        self.protected.add(user) if sec == self.secret else print("That's wrong!")


def main():
    info = Info()
    while True:
        print('1. read list |==| 2. add user |==| 3. quit')
        key = input('choose option: ')
        if key == '1':
            info.read()
        elif key == '2':
            name = input('choose username: ')
            info.add(name)
        elif key == '3':
            exit()
        else:
            print('unknown option: {}'.format(key))

if __name__ == '__main__':
    main()

行为型模式，介绍处理系统实体之间通信的设计模式

责任链（Chain of Responsibility）模式

用于让多个对象来处理单个请求 时，或者用于预先不知道应该由哪个对象（来自某个对象链）来处理某个特定请求时。

 可以使用广播计算机网络的类比来理解责任链模式

# Author:song

"""
MainWindow、MsgText和SendDialog是具有不同行为的控件,
MainWindow仅能处理close和default事件,
SendDialog仅能处理paint事件,
MsgText仅能处理down事件
main()函数展示如何创建一些控件和事件，以及控件如何对那些事件作出反应。
所有事件都会被发送给所有控件
"""
class Event:

    def __init__(self, name):
        self.name = name

    def __str__(self):
        return self.name


class Widget:

    def __init__(self, parent=None):
        self.parent = parent

    def handle(self, event):
        """handle()方法使用动态分发，通过hasattr()和getattr()决定一个特定请求（event）
应该由谁来处理。如果被请求处理事件的控件并不支持该事件，则有两种回退机制。如果控件有
parent，则执行parent的handle()方法。如果控件没有parent，但有handle_default()方
法，则执行handle_default()。"""
        handler = 'handle_{}'.format(event)
        if hasattr(self, handler):
            method = getattr(self, handler)
            method(event)
        elif self.parent:
            self.parent.handle(event)
        elif hasattr(self, 'handle_default'):
            self.handle_default(event)


class MainWindow(Widget):

    def handle_close(self, event):
        print('MainWindow: {}'.format(event))

    def handle_default(self, event):
        print('MainWindow Default: {}'.format(event))


class SendDialog(Widget):

    def handle_paint(self, event):
        print('SendDialog: {}'.format(event))


class MsgText(Widget):

    def handle_down(self, event):
        print('MsgText: {}'.format(event))


def main():
    mw = MainWindow()
    sd = SendDialog(mw)
    msg = MsgText(sd)

    for e in ('down', 'paint', 'unhandled', 'close'):
        evt = Event(e)
        print('
Sending event -{}- to MainWindow'.format(evt))
        mw.handle(evt)
        print('Sending event -{}- to SendDialog'.format(evt))
        sd.handle(evt)
        print('Sending event -{}- to MsgText'.format(evt))
        msg.handle(evt)

if __name__ == '__main__':
    main()

命令设计模式

帮助我们将一个操作（撤销、重做、复制、粘贴等）封装成一个对象。简而言之，这意味着创建一个类，包含实现该操作所需要的所有逻辑和方法.

撤销操作确实是命令模式的杀手级特性。

优势：

 我们并不需要直接执行一个命令。命令可以按照希望执行。

 调用命令的对象与知道如何执行命令的对象解耦。调用者无需知道命令的任何实现细节。

 如果有意义，可以把多个命令组织起来，这样调用者能够按顺序执行它们。例如，在实 现一个多层撤销命令时，这是很有用的。

# Author:song
import os

verbose = True


class RenameFile:

    def __init__(self, path_src, path_dest):
        self.src, self.dest = path_src, path_dest

    def execute(self):
        if verbose:
            print("[renaming '{}' to '{}']".format(self.src, self.dest))
        os.rename(self.src, self.dest)

    def undo(self):
        """通过undo()方法支持撤销操作。在这里，撤销操作再次使用os.rename()
将文件名恢复为原始值。"""
        if verbose:
            print("[renaming '{}' back to '{}']".format(self.dest, self.src))
        os.rename(self.dest, self.src)


class CreateFile:
    """。__init__()函数接受熟悉的
path参数和一个txt字符串，默认向文件写入hello world文本"""
    def __init__(self, path, txt='hello world
'):
        self.path, self.txt = path, txt

    def execute(self):
        if verbose:
            print("[creating file '{}']".format(self.path))
        with open(self.path, mode='w', encoding='utf-8') as out_file:
            out_file.write(self.txt)

    def undo(self):
        delete_file(self.path)


class ReadFile:

    def __init__(self, path):
        self.path = path

    def execute(self):
        if verbose:
            print("[reading file '{}']".format(self.path))
        with open(self.path, mode='r', encoding='utf-8') as in_file:
            print(in_file.read(), end='')


def delete_file(path):
    """数接受一个字符串类型的文件路
径，并使用os.remove()来删除它"""
    if verbose:
        print("deleting file '{}'".format(path))
    os.remove(path)


def main():
    """main()函数使用这些工具类/方法。参数orig_name和new_name是待创建文件的原始名称
以及重命名后的新名称。commands列表用于添加（并配置）所有我们之后想要执行的命令。注
意，命令不会被执行，除非我们显式地调用每个命令的execute()
下一步是询问用户是否需要撤销执行过的命令。用户选择撤销命令或不撤销。如果选择撤销，
则执行commands列表中所有命令的undo()。然而，由于并不是所有命令都支持撤销，因此在
undo()方法不存在时产生的AttributeError异常要使用异常处理来捕获
"""
    orig_name, new_name = 'file1', 'file2'

    commands = []
    for cmd in CreateFile(orig_name), ReadFile(orig_name), RenameFile(orig_name, new_name):
        commands.append(cmd)

    [c.execute() for c in commands]

    answer = input('reverse the executed commands? [y/n] ')

    if answer not in 'yY':
        print("the result is {}".format(new_name))
        exit()

    for c in reversed(commands):
        try:
            c.undo()
        except AttributeError as e:
            pass

if __name__ == '__main__':
    main()

解释器（Interpreter）模式

解释器模式仅能引起应用的高级用户的兴趣。这是因为解释器模式背后的主 要思想是让非初级用户和领域专家使用一门简单的语言来表达想法.

解释器模式用于为高级用户和领域专家提供一个类编程的框架，但没有暴露出编程语言那样的复杂性.

对每个应用来说，至少有以下两种不同的用户分类。

 基本用户：这类用户只希望能够凭直觉使用应用。他们不喜欢花太多时间配置或学习应 用的内部。对他们来说，基本的用法就足够了。

 高级用户：这些用户，实际上通常是少数，不介意花费额外的时间学习如何使用应用的 高级特性。如果知道学会之后能得到以下好处，他们甚至会去学习一种配置（或脚本） 语言。

# Author:song
# coding: utf-8
"""使用了Pyparsing创建一种
DSL来控制一个智能屋，并且看到使用一个好的解析工具以模式匹配来解释结果更加简单"""
from pyparsing import Word, OneOrMore, Optional, Group, Suppress, alphanums


class Gate:

    def __init__(self):
        self.is_open = False

    def __str__(self):
        return 'open' if self.is_open else 'closed'

    def open(self):
        print('opening the gate')
        self.is_open = True

    def close(self):
        print('closing the gate')
        self.is_open = False


class Garage:

    def __init__(self):
        self.is_open = False

    def __str__(self):
        return 'open' if self.is_open else 'closed'

    def open(self):
        print('opening the garage')
        self.is_open = True

    def close(self):
        print('closing the garage')
        self.is_open = False


class Aircondition:

    def __init__(self):
        self.is_on = False

    def __str__(self):
        return 'on' if self.is_on else 'off'

    def turn_on(self):
        print('turning on the aircondition')
        self.is_on = True

    def turn_off(self):
        print('turning off the aircondition')
        self.is_on = False


class Heating:

    def __init__(self):
        self.is_on = False

    def __str__(self):
        return 'on' if self.is_on else 'off'

    def turn_on(self):
        print('turning on the heating')
        self.is_on = True

    def turn_off(self):
        print('turning off the heating')
        self.is_on = False


class Boiler:

    def __init__(self):
        self.temperature = 83  # in celsius

    def __str__(self):
        return 'boiler temperature: {}'.format(self.temperature)

    def increase_temperature(self, amount):
        print("increasing the boiler's temperature by {} degrees".format(amount))
        self.temperature += amount

    def decrease_temperature(self, amount):
        print("decreasing the boiler's temperature by {} degrees".format(amount))
        self.temperature -= amount


class Fridge:

    def __init__(self):
        self.temperature = 2  # 单位为摄氏度

    def __str__(self):
        return 'fridge temperature: {}'.format(self.temperature)

    def increase_temperature(self, amount):
        print("increasing the fridge's temperature by {} degrees".format(amount))
        self.temperature += amount

    def decrease_temperature(self, amount):
        print("decreasing the fridge's temperature by {} degrees".format(amount))
        self.temperature -= amount


def main():
    word = Word(alphanums)
    command = Group(OneOrMore(word))
    token = Suppress("->")
    device = Group(OneOrMore(word))
    argument = Group(OneOrMore(word))
    event = command + token + device + Optional(token + argument)

    gate = Gate()
    garage = Garage()
    airco = Aircondition()
    heating = Heating()
    boiler = Boiler()
    fridge = Fridge()

    tests = ('open -> gate',
             'close -> garage',
             'turn on -> aircondition',
             'turn off -> heating',
             'increase -> boiler temperature -> 5 degrees',
             'decrease -> fridge temperature -> 2 degrees')
    open_actions = {'gate': gate.open,
                    'garage': garage.open,
                    'aircondition': airco.turn_on,
                    'heating': heating.turn_on,
                    'boiler temperature': boiler.increase_temperature,
                    'fridge temperature': fridge.increase_temperature}
    close_actions = {'gate': gate.close,
                     'garage': garage.close,
                     'aircondition': airco.turn_off,
                     'heating': heating.turn_off,
                     'boiler temperature': boiler.decrease_temperature,
                     'fridge temperature': fridge.decrease_temperature}

    for t in tests:
        if len(event.parseString(t)) == 2:  # 没有参数
            cmd, dev = event.parseString(t)
            cmd_str, dev_str = ' '.join(cmd), ' '.join(dev)
            if 'open' in cmd_str or 'turn on' in cmd_str:
                open_actions[dev_str]()
            elif 'close' in cmd_str or 'turn off' in cmd_str:
                close_actions[dev_str]()
        elif len(event.parseString(t)) == 3:  # 有参数
            cmd, dev, arg = event.parseString(t)
            cmd_str, dev_str, arg_str = ' '.join(cmd), ' '.join(dev), ' '.join(arg)
            num_arg = 0
            try:
                num_arg = int(arg_str.split()[0])  # 抽取数值部分
            except ValueError as err:
                print("expected number but got: '{}'".format(arg_str[0]))
            if 'increase' in cmd_str and num_arg > 0:
                open_actions[dev_str](num_arg)
            elif 'decrease' in cmd_str and num_arg > 0:
                close_actions[dev_str](num_arg)

if __name__ == '__main__':
    main()

 

观察者模式

我们希望在一个对象的状态改变时更新另外一组对象,观察者模式描述单个对象（发布者，又称为主持者或可观察者）与一个或多个对象（订阅者， 又称为观察者）之间的发布—订阅关系。

观察者模式背后的思想等同于MVC和关注点分离原则背后的思想，即降低发布者与订阅者 之间的耦合度，从而易于在运行时添加/删除订阅者。此外，发布者不关心它的订阅者是谁。它只是将通知发送给所有订阅者。

若希望在一个对象的状态变化时能够通知/提醒所有 相关者（一个对象或一组对象），则可以使用观察者模式。观察者模式的一个重要特性是，在运行时，订阅者/观察者的数量以及观察者是谁可能会变化，也可以改变

# Author:song
class Publisher:

    def __init__(self):
        self.observers = []

    def add(self, observer):
        if observer not in self.observers:
            self.observers.append(observer)
        else:
            print('Failed to add: {}'.format(observer))

    def remove(self, observer):
        try:
            self.observers.remove(observer)
        except ValueError:
            print('Failed to remove: {}'.format(observer))

    def notify(self):
        [o.notify(self) for o in self.observers]


class DefaultFormatter(Publisher):

    def __init__(self, name):
        Publisher.__init__(self)
        self.name = name
        self._data = 0

    def __str__(self):
        return "{}: '{}' has data = {}".format(type(self).__name__, self.name, self._data)

    @property
    def data(self):
        return self._data

    @data.setter
    def data(self, new_value):
        try:
            self._data = int(new_value)
        except ValueError as e:
            print('Error: {}'.format(e))
        else:
            self.notify()


class HexFormatter:

    def notify(self, publisher):
        print("{}: '{}' has now hex data = {}".format(type(self).__name__,
                                                      publisher.name, hex(publisher.data)))


class BinaryFormatter:

    def notify(self, publisher):
        print("{}: '{}' has now bin data = {}".format(type(self).__name__,
                                                      publisher.name, bin(publisher.data)))


def main():
    df = DefaultFormatter('test1')
    print(df)

    print()
    hf = HexFormatter()
    df.add(hf)
    df.data = 3
    print(df)

    print()
    bf = BinaryFormatter()
    df.add(bf)
    df.data = 21
    print(df)

    print()
    df.remove(hf)
    df.data = 40
    print(df)

    print()
    df.remove(hf)
    df.add(bf)
    df.data = 'hello'
    print(df)

    print()
    df.data = 15.8
    print(df)

if __name__ == '__main__':
    main()

面向对象编程

面向对象编程着力于在对象交互时改变它们的状态,状态机是一个抽象机器，有两个关键部分，状态和转换。状态是指系统的当前（激活） 状况,转换是指从一个状态切换 到另一个状态，因某个事件或条件的触发而开始。通常，在一次转换发生之前或之后会执行一个 或一组动作.

状态模式是一个或多个有限状态机（简称状态机）的实现，用于解决一个特定的软件工程问题

# Author:song
from state_machine import State, Event, acts_as_state_machine, after, before, InvalidStateTransition


@acts_as_state_machine
class Process:
    created = State(initial=True)
    waiting = State()
    running = State()
    terminated = State()
    blocked = State()
    swapped_out_waiting = State()
    swapped_out_blocked = State()

    wait = Event(from_states=(created, running, blocked,
                              swapped_out_waiting), to_state=waiting)
    run = Event(from_states=waiting, to_state=running)
    terminate = Event(from_states=running, to_state=terminated)
    block = Event(from_states=(running, swapped_out_blocked),
                  to_state=blocked)
    swap_wait = Event(from_states=waiting, to_state=swapped_out_waiting)
    swap_block = Event(from_states=blocked, to_state=swapped_out_blocked)

    def __init__(self, name):
        self.name = name

    @after('wait')
    def wait_info(self):
        print('{} entered waiting mode'.format(self.name))

    @after('run')
    def run_info(self):
        print('{} is running'.format(self.name))

    @before('terminate')
    def terminate_info(self):
        print('{} terminated'.format(self.name))

    @after('block')
    def block_info(self):
        print('{} is blocked'.format(self.name))

    @after('swap_wait')
    def swap_wait_info(self):
        print('{} is swapped out and waiting'.format(self.name))

    @after('swap_block')
    def swap_block_info(self):
        print('{} is swapped out and blocked'.format(self.name))


def transition(process, event, event_name):
    try:
        event()
    except InvalidStateTransition as err:
        print('Error: transition of {} from {} to {} failed'.format(process.name,
                                                                    process.current_state, event_name))


def state_info(process):
    print('state of {}: {}'.format(process.name, process.current_state))


def main():
    RUNNING = 'running'
    WAITING = 'waiting'
    BLOCKED = 'blocked'
    TERMINATED = 'terminated'

    p1, p2 = Process('process1'), Process('process2')
    [state_info(p) for p in (p1, p2)]

    print()
    transition(p1, p1.wait, WAITING)
    transition(p2, p2.terminate, TERMINATED)
    [state_info(p) for p in (p1, p2)]

    print()
    transition(p1, p1.run, RUNNING)
    transition(p2, p2.wait, WAITING)
    [state_info(p) for p in (p1, p2)]

    print()
    transition(p2, p2.run, RUNNING)
    [state_info(p) for p in (p1, p2)]

    print()
    [transition(p, p.block, BLOCKED) for p in (p1, p2)]
    [state_info(p) for p in (p1, p2)]

    print()
    [transition(p, p.terminate, TERMINATED) for p in (p1, p2)]
    [state_info(p) for p in (p1, p2)]

if __name__ == '__main__':
    main()

策略模式
策略模式（Strategy pattern）鼓励使用多种算法来解决一个问题，其杀手级特性是能够在运 行时透明地切换算法（客户端代码对变化无感知）。因此，如果你有两种算法，并且知道其中一 种对少量输入效果更好，另一种对大量输入效果更好，则可以使用策略模式在运行时基于输入数据决定使用哪种算法

策略模式的另一个应用是创建不同的样式表现，为了实现可移植性（例如，不同平台之间断行的不同）或动态地改变数据的表现.

# Author:song
# coding: utf-8

import time
SLOW = 3  # 单位为秒
LIMIT = 5   # 字符数
WARNING = 'too bad, you picked the slow algorithm :('


def pairs(seq):
    n = len(seq)
    for i in range(n):
        yield seq[i], seq[(i + 1) % n]


def allUniqueSort(s):
    if len(s) > LIMIT:
        print(WARNING)
        time.sleep(SLOW)
    srtStr = sorted(s)
    for (c1, c2) in pairs(srtStr):
        if c1 == c2:
            return False
    return True


def allUniqueSet(s):
    if len(s) < LIMIT:
        print(WARNING)
        time.sleep(SLOW)
    return True if len(set(s)) == len(s) else False


def allUnique(s, strategy):
    return strategy(s)


def main():
    while True:
        word = None
        while not word:
            word = input('Insert word (type quit to exit)> ')
            if word == 'quit':
                print('bye')
                return

            strategy_picked = None
            strategies = {'1': allUniqueSet, '2': allUniqueSort}
            while strategy_picked not in strategies.keys():
                strategy_picked = input('Choose strategy: [1] Use a set, [2] Sort and pair> ')

                try:
                    strategy = strategies[strategy_picked]
                    print('allUnique({}): {}'.format(word, allUnique(word, strategy)))
                except KeyError as err:
                    print('Incorrect option: {}'.format(strategy_picked))

if __name__ == '__main__':
    main()

模板设计模式

模板设计模式旨在消除代码重复。如果我们发现结构相近的（多个）算法中有重复代码，则可以把算法的不变（通用）部分留在一个模板方法/函数中，把易变（不同的部分移到动作/钩子方法/函数中

在实现结构相近的算法时，可以使用模板模式来消除冗余代码。具体实现方式是使用动作/钩子方法/函数来完成代码重复的消除.

# Author:song
from cowpy import cow

"""实现一个横幅生成器。想法很简单，将一段文本发送给一个函数，该函数要
生成一个包含该文本的横幅。横幅有多种风格，比如点或虚线围绕文本。横幅生成器有一个默认
风格，但应该能够使用我们自己提供的风格函数generate_banner()是我们的模板函数。它接受一个输入参数（msg，希望横幅包含
的文本）和一个可选参数（style，希望使用的风格）。默认风格是dots_style"""


def dots_style(msg):
    msg = msg.capitalize()
    msg = '.' * 10 + msg + '.' * 10
    return msg


def admire_style(msg):
    msg = msg.upper()
    return '!'.join(msg)


def cow_style(msg):
    msg = cow.milk_random_cow(msg)
    return msg


def generate_banner(msg, style=dots_style):
    print('-- start of banner --')
    print(style(msg))
    print('-- end of banner --

')


def main():
    """main()函数向横幅发送文本“happy coding”，并使用所有可用风格将横幅输出到标准输出"""
    msg = 'happy coding'
    [generate_banner(msg, style) for style in (dots_style, admire_style, cow_style)]

if __name__ == '__main__':
    main()

参考文献：

《Python设计模式》