[Programming Ideas] [Design Patterns] Factory Patterns

Python version

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

 

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

"""*What is this pattern about?
>> what does this design pattern do
The Factory Method pattern can be used to create an interface for a
method, leaving the implementation to the class that gets
instantiated.
>> This design pattern can create an interface for the method and let other inherited classes implement it

*What does this example do?
The code shows a way to localize words in two languages: English and
Greek.
>> This code means to translate the word into two languages, English and Greek
"getLocalizer" is the factory method that constructs a
localizer depending on the language chosen.
"getLocalizer" is the factory method that builds the Localizer depending on the language chosen
The localizer object will
be an instance from a different class according to the language
localized.
>>Localizer objects become different instances depending on the language translator selected
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.
>> However, the main program is different about which translator will be used, because the get method will be called differently depending on the language selected

*Where can the pattern be used practically?
>> where will this design pattern be used
The Factory Method can be seen in the popular web framework Django:
>> In the very process Django web framework, we can often see the factory pattern
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.
>> For example at http://django.wikispaces.asu.edu/*NEW*+Django+Design+Patterns,
>> In the contact form of the web page, the place for subject and message is to use the same form factory (CharField()),
>> though it looks like they have different implementations

*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 dog 
# parrot parrot 
# cat cat 
# bear bear

Python reprint version

 

Python version

big talk design pattern