精通Python设计模式第二版第 1 章工厂模式学习笔记

工厂模式

工厂模式的思想意在简化对象的创建过程。调用者（客户端）不清楚对象的来源以及生成对象的方式，调用者只需要调用某个方法或者实例某个类既可以获得想要对象。这些对象根据不同的生产需求而产生

两种形式

工厂方法：一个方法（或者说函数）根据不同的输入参数返回不同的对象
抽象工厂：一组用于创建一系列相关对象的工厂方法

工厂方法的实现

让我们想象一下这样一个需求，我们有一些数据文件需要分析，分别是XML和JSON。这两种文件需要不容的库解析数据，但是调用者不想关心，然后区分处理这两种数据。这种场景需求就可以使用工厂方法来解决，工厂方法会帮我们做好不同数据格式的数据解析。

让我们先看一下需要解析的文件数据

movies.json

[{"title": "After Dark in Central Park","year": 1900,"director": null,"cast": null,"genre": null},{"title": "Boarding School Girls' Pajama Parade","year": 1900,"director": null,"cast": null,"genre": null},{"title": "Buffalo Bill's Wild West Parad","year": 1900,"director": null,"cast": null,"genre": null},{"title": "Caught","year": 1900,"director": null,"cast": null,"genre": null},{"title": "Clowns Spinning Hats","year": 1900,"director": null,"cast": null,"genre": null},{"title": "Capture of Boer Battery by British","year": 1900,"director": "James H. White","cast": null,"genre": "Short documentary"},{"title": "The Enchanted Drawing","year": 1900,"director": "J. Stuart Blackton","cast": null,"genre": null},{"title": "Family Troubles","year": 1900,"director": null,"cast": null,"genre": null},{"title": "Feeding Sea Lions","year": 1900,"director": null,"cast": "Paul Boyton","genre": null}
]

person.xml

<persons><person><firstName>John</firstName><lastName>Smith</lastName><age>25</age><address><streetAddress>21 2nd Street</streetAddress><city>New York</city><state>NY</state><postalCode>10021</postalCode></address><phoneNumbers><phoneNumber type="home">212 555-1234</phoneNumber><phoneNumber type="fax">646 555-4567</phoneNumber></phoneNumbers><gender><type>male</type></gender></person><person><firstName>Jimy</firstName><lastName>Liar</lastName><age>19</age><address><streetAddress>18 2nd Street</streetAddress><city>New York</city><state>NY</state><postalCode>10021</postalCode></address><phoneNumbers><phoneNumber type="home">212 555-1234</phoneNumber></phoneNumbers><gender><type>male</type></gender></person><person><firstName>Patty</firstName><lastName>Liar</lastName><age>20</age><address><streetAddress>18 2nd Street</streetAddress><city>New York</city><state>NY</state><postalCode>10021</postalCode></address><phoneNumbers><phoneNumber type="home">212 555-1234</phoneNumber><phoneNumber type="mobile">001 452-8819</phoneNumber></phoneNumbers><gender><type>female</type></gender></person>
</persons>

接下来，让我们看看如何实现这样一个工厂方法

1. 先找到能解析这两种数据的库

import json
import xml.etree.ElementTree as etree

2. 解析数据的方法

类JSONDataExtractor用于解析JSON文件，它有parsed_data()方法，返回一个包含所有数据的字典。
类XMLDataExtractor则用于解析XML文件

class JSONDataExtractor:"""JSONDataExtractor : 用于解析JSON文件Attributes:"""def __init__(self, filepath):self.data = dict()  # 包含所有数据的字典with open(filepath, 'r', encoding='utf8') as f:self.data = json.load(f)@propertydef parsed_data(self):return self.dataclass XMLDataExtractor():"""XMLDataExtractor : 用于解析XML文件Attributes:"""def __init__(self, filepath):self.tree = etree.parse(filepath)@propertydef parsed_data(self):return self.tree

3. 工厂方法

根据输入文件的拓展名，返回一个JSONDataExtractor或XMLDataExtractor的实例

def dataextraction_factory(filepath):'''工厂方法 根据输入文件的拓展名，返回一个JSONDataExtractor或XMLDataExtractor的实例:param filepath::return:'''if filepath.endswith('json'):extractor = JSONDataExtractorelif filepath.endswith('xml'):extractor = XMLDataExtractorelse:raise ValueError('Cannot extract data from {}'.format(filepath))return extractor(filepath)

4. 最后添加一些异常处理机制

def extract_data_from(filepath):'''dataextraction_factory() 方法的装饰器。它增加了异常处理机制:param filepath::return:'''factory_obj = Nonetry:factory_obj = dataextraction_factory(filepath)except ValueError as e:print(e)return factory_obj

5. 工厂函数的使用

def main():# 展示如果使用 工厂方法处理JSON文件json_factory = extract_data_from('data/movies.json')json_data = json_factory.parsed_dataprint(f'Found: {len(json_data)} movies')for movie in json_data:print(f"Title: {movie['title']}")year = movie['year']if year:print(f"Year: {year}")director = movie['director']if director:print(f"Director: {director}")genre = movie['genre']if genre:print(f"Genre: {genre}")print()# 展示如何使用工厂方法处理XML文件xml_factory = extract_data_from('data/person.xml')xml_data = xml_factory.parsed_dataliars = xml_data.findall(f".//person[lastName='Liar']")print(f'found: {len(liars)} persons')for liar in liars:firstname = liar.find('firstName').textprint(f'first name: {firstname}')lastname = liar.find('lastName').textprint(f'last name: {lastname}')[print(f"phone number ({p.attrib['type']}):", p.text)for p in liar.find('phoneNumbers')]print()print()if __name__ == '__main__':main()

获得的打印如下

Found: 9 movies
Title: After Dark in Central Park
Year: 1900Title: Boarding School Girls' Pajama Parade
Year: 1900Title: Buffalo Bill's Wild West Parad
Year: 1900Title: Caught
Year: 1900Title: Clowns Spinning Hats
Year: 1900Title: Capture of Boer Battery by British
Year: 1900
Director: James H. White
Genre: Short documentaryTitle: The Enchanted Drawing
Year: 1900
Director: J. Stuart BlacktonTitle: Family Troubles
Year: 1900Title: Feeding Sea Lions
Year: 1900found: 2 persons
first name: Jimy
last name: Liar
phone number (home): 212 555-1234first name: Patty
last name: Liar
phone number (home): 212 555-1234
phone number (mobile): 001 452-8819

工厂方法完整代码

factory_method.py

import json
import xml.etree.ElementTree as etreeclass JSONDataExtractor:"""JSONDataExtractor : 用于解析JSON文件Attributes:"""def __init__(self, filepath):self.data = dict()  # 包含所有数据的字典with open(filepath, 'r', encoding='utf8') as f:self.data = json.load(f)@propertydef parsed_data(self):return self.dataclass XMLDataExtractor():"""XMLDataExtractor : 用于解析XML文件Attributes:"""def __init__(self, filepath):self.tree = etree.parse(filepath)@propertydef parsed_data(self):return self.treedef dataextraction_factory(filepath):'''工厂方法 根据输入文件的拓展名，返回一个JSONDataExtractor或XMLDataExtractor的实例:param filepath::return:'''if filepath.endswith('json'):extractor = JSONDataExtractorelif filepath.endswith('xml'):extractor = XMLDataExtractorelse:raise ValueError('Cannot extract data from {}'.format(filepath))return extractor(filepath)def extract_data_from(filepath):'''dataextraction_factory() 方法的装饰器。它增加了异常处理机制:param filepath::return:'''factory_obj = Nonetry:factory_obj = dataextraction_factory(filepath)except ValueError as e:print(e)return factory_objdef main():# sqlite_factory = extract_data_from('data/person.sq3')# print()# 展示如果使用 工厂方法处理JSON文件json_factory = extract_data_from('data/movies.json')json_data = json_factory.parsed_dataprint(f'Found: {len(json_data)} movies')for movie in json_data:print(f"Title: {movie['title']}")year = movie['year']if year:print(f"Year: {year}")director = movie['director']if director:print(f"Director: {director}")genre = movie['genre']if genre:print(f"Genre: {genre}")print()# 展示如何使用工厂方法处理XML文件xml_factory = extract_data_from('data/person.xml')xml_data = xml_factory.parsed_dataliars = xml_data.findall(f".//person[lastName='Liar']")print(f'found: {len(liars)} persons')for liar in liars:firstname = liar.find('firstName').textprint(f'first name: {firstname}')lastname = liar.find('lastName').textprint(f'last name: {lastname}')[print(f"phone number ({p.attrib['type']}):", p.text)for p in liar.find('phoneNumbers')]print()print()if __name__ == '__main__':main()

抽象工厂的实现

假设我们正在创建一个游戏，或者想将一个迷你游戏作为应用程序的一部分来取悦用户。我们希望至少包括两款游戏：一款儿童游戏，一款成人游戏。我们将根据用户的输入，在运行时决定创建和启动哪款游戏

1. 儿童游戏的创建

男主角是一只喜欢吃虫子的青蛙，每一个主角都需要一个好的名字

class Frog():"""Frog :Attributes:"""def __init__(self, name):self.name = namedef __str__(self):return self.namedef interact_with(self, obstacle):'''用于描述 青蛙和障碍物之间的交互:param obstacle::return:'''act = obstacle.action()msg = f'{self} the Frog encounters {obstacle} and {act} !'print(msg)class Bug():"""Bug :Attributes:"""def __str__(self):return 'a bug'def action(self):'''青蛙只支持一种行为：吃掉虫子'''return 'eats it'

2. 儿童游戏的抽象工厂

它的主要任务是创建游戏中的主角与障碍物。保持创建方法的独立性以及名称的通用性

class FrogWorld():"""FrogWorld : 抽象工厂。它的主要任务是创建游戏中的主角与障碍物Attributes:"""def __init__(self, name):print(self)self.player_name = namedef __str__(self):return '\n\n\t------ Frog World ------'def make_character(self):return Frog(self.player_name)def make_obstacle(self):return Bug()

3. 成人游戏的创建

跟儿童游戏的区别是，这是一个巫师打兽人的游戏

class Wizard():"""Wizard :Attributes:"""def __init__(self, name):self.name = namedef __str__(self):return self.namedef interact_with(self, obstacle):act = obstacle.action()msg = f'{self} the Wizard battles against {obstacle} and {act}!'print(msg)class Ork():"""Ork :Attributes:"""def __str__(self):return 'an evil ork'def action(self):return 'kills it'

4. 成人游戏的抽象工厂

情况与儿童游戏类似

class WizardWorld():"""WizardWorld :Attributes:"""def __init__(self, name):print(self)self.player_name = namedef __str__(self):return '\n\n\t------ Wizard World ------'def make_character(self):return Wizard(self.player_name)def make_obstacle(self):return Ork()

5. 游戏的主入口

接收一个工厂作为输入，并使用它来创建游戏世界

class GameEnvironment():"""GameEnvironment : 游戏的主入口。它接收一个工厂作为输入，并使用它来创建游戏世界Attributes:"""def __init__(self, facotry):self.hero = facotry.make_character()self.obstacle = facotry.make_obstacle()def play(self):'''初始化主角与障碍物之间的交互:return:'''self.hero.interact_with(self.obstacle)

6. 游戏创建逻辑

def validate_age(name):'''提示用户给出一个有效年龄。如果年龄无效，则返回一个首元素为False的元祖:param name::return:'''try:age = input(f'Welcome {name}. How old are you? \n')age = int(age)except ValueError as err:print(f'Age {age} is invalid, please try again...')return (False, age)return (True, age)

7. 游戏运行逻辑

def main():'''询问用户姓名和年龄，并根据用户的年龄决定应该玩哪款游戏:return:'''name = input("Hello, What's your name? \n")valid_input = Falsewhile not valid_input:valid_input, age = validate_age(name)game = FrogWorld if age < 18 else WizardWorldenvironment = GameEnvironment(game(name))environment.play()if __name__ == '__main__':main()

获取打印如下

Hello, What's your name?
coco
Welcome coco. How old are you?
19------ Wizard World ------
coco the Wizard battles against an evil ork and kills it!

抽象工厂完整代码

class Frog():"""Frog :Attributes:"""def __init__(self, name):self.name = namedef __str__(self):return self.namedef interact_with(self, obstacle):'''用于描述 青蛙和障碍物之间的交互:param obstacle::return:'''act = obstacle.action()msg = f'{self} the Frog encounters {obstacle} and {act} !'print(msg)class Bug():"""Bug :Attributes:"""def __str__(self):return 'a bug'def action(self):'''青蛙只支持一种行为：吃掉虫子'''return 'eats it'class FrogWorld():"""FrogWorld : 抽象工厂。它的主要任务是创建游戏中的主角与障碍物Attributes:"""def __init__(self, name):print(self)self.player_name = namedef __str__(self):return '\n\n\t------ Frog World ------'def make_character(self):return Frog(self.player_name)def make_obstacle(self):return Bug()class Wizard():"""Wizard :Attributes:"""def __init__(self, name):self.name = namedef __str__(self):return self.namedef interact_with(self, obstacle):act = obstacle.action()msg = f'{self} the Wizard battles against {obstacle} and {act}!'print(msg)class Ork():"""Ork :Attributes:"""def __str__(self):return 'an evil ork'def action(self):return 'kills it'class WizardWorld():"""WizardWorld :Attributes:"""def __init__(self, name):print(self)self.player_name = namedef __str__(self):return '\n\n\t------ Wizard World ------'def make_character(self):return Wizard(self.player_name)def make_obstacle(self):return Ork()class GameEnvironment():"""GameEnvironment : 游戏的主入口。它接收一个工厂作为输入，并使用它来创建游戏世界Attributes:"""def __init__(self, facotry):self.hero = facotry.make_character()self.obstacle = facotry.make_obstacle()def play(self):'''初始化主角与障碍物之间的交互:return:'''self.hero.interact_with(self.obstacle)def validate_age(name):'''提示用户给出一个有效年龄。如果年龄无效，则返回一个首元素为False的元祖:param name::return:'''try:age = input(f'Welcome {name}. How old are you? \n')age = int(age)except ValueError as err:print(f'Age {age} is invalid, please try again...')return (False, age)return (True, age)def main():'''询问用户姓名和年龄，并根据用户的年龄决定应该玩哪款游戏:return:'''name = input("Hello, What's your name? \n")valid_input = Falsewhile not valid_input:valid_input, age = validate_age(name)game = FrogWorld if age < 18 else WizardWorldenvironment = GameEnvironment(game(name))environment.play()if __name__ == '__main__':main()

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