【编程思想】【设计模式】【创建模式creational 】工厂模式factory_method

Python版

https://github.com/faif/python-patterns/blob/master/creational/factory_method.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""*What is this pattern about?
>>这个设计模式是干什么的
The Factory Method pattern can be used to create an interface for a
method, leaving the implementation to the class that gets
instantiated.
>>这个设计模式可以为方法创建一个接口，让其他继承的类来实现

*What does this example do?
The code shows a way to localize words in two languages: English and
Greek.
>>这个代码表示把单词翻译成两种语言，英语和希腊语
"getLocalizer" is the factory method that constructs a
localizer depending on the language chosen.
“getLocalizer”是工厂方法，他根据选择的语言的不同，构建Localizer
The localizer object will
be an instance from a different class according to the language
localized.
>>Localizer对象根据选择语言翻译器的不同，成为不同的实例
However, the main code does not have to worry about which
localizer will be instantiated, since the method "get" will be called
in the same way independently of the language.
>>但是，主要程序不同担心哪个翻译器会被实力话，因为get方法会根据选择语言的不同有不同的调用

*Where can the pattern be used practically?
>>这个设计模式会被用在什么地方
The Factory Method can be seen in the popular web framework Django:
>>在非常流程的Django网络框架中，我们经常可以看到工厂模式
http://django.wikispaces.asu.edu/*NEW*+Django+Design+Patterns For
example, in a contact form of a web page, the subject and the message
fields are created using the same form factory (CharField()), even
though they have different implementations according to their
purposes.
>>例如在http://django.wikispaces.asu.edu/*NEW*+Django+Design+Patterns，
>>在网页的联系表中，主题和消息的地方就是使用相同的表格工厂(CharField())，
>>尽管看起来他们有不同的实现方式

*References:
http://ginstrom.com/scribbles/2007/10/08/design-patterns-python-style/
https://fkromer.github.io/python-pattern-references/design/#factory-method
https://sourcemaking.com/design_patterns/factory_method

*TL;DR80
Creates objects without having to specify the exact class.
"""

class GreekGetter(object):

    """A simple localizer a la gettext"""

    def __init__(self):
        self.trans = dict(dog="σκύλος", cat="γάτα")

    def get(self, msgid):
        """We'll punt if we don't have a translation"""
        return self.trans.get(msgid, str(msgid))

class EnglishGetter(object):

    """Simply echoes the msg ids"""

    def get(self, msgid):
        return str(msgid)

def get_localizer(language="English"):
    """The factory method"""
    languages = dict(English=EnglishGetter, Greek=GreekGetter)
    return languages[language]()

if __name__ == '__main__':
    # Create our localizers
    e, g = get_localizer(language="English"), get_localizer(language="Greek")
    # Localize some text
    for msgid in "dog parrot cat bear".split():
        print(e.get(msgid), g.get(msgid))

### OUTPUT ###
# dog σκύλος
# parrot parrot
# cat γάτα
# bear bear

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