9.3. Factory Method

9.3.1. Rationale

  • EN: Factory Method

  • PL: Metoda wytwórcza

  • Type: class

9.3.2. Use Cases

9.3.3. Design

9.3.4. Implementation

class Setosa:
    pass

class Versicolor:
    pass

class Virginica:
    pass


def iris_factory(species):
    if species == 'setosa':
        return Setosa
    elif species == 'versicolor':
        return Versicolor
    elif species == 'virginica':
        return Virginica
    else:
        raise NotImplementedError


if __name__ == '__main__':
    iris = iris_factory('setosa')
    print(iris)
    # <class '__main__.Setosa'>

    iris = iris_factory('virginica')
    print(iris)
    # <class '__main__.Virginica'>

    iris = iris_factory('arctica')
    print(iris)
    # Traceback (most recent call last):
    # NotImplementedError
class Setosa:
    pass

class Versicolor:
    pass

class Virginica:
    pass


def iris_factory(species):
    cls = {
        'setosa': Setosa,
        'versicolor': Versicolor,
        'virginica': Virginica,
    }.get(species, None)

    if not cls:
        raise NotImplementedError
    else:
        return cls


if __name__ == '__main__':
    iris = iris_factory('setosa')
    print(iris)
    # <class '__main__.Setosa'>

    iris = iris_factory('virginica')
    print(iris)
    # <class '__main__.Virginica'>

    iris = iris_factory('arctica')
    print(iris)
    # Traceback (most recent call last):
    # NotImplementedError
class Setosa:
    pass

class Virginica:
    pass

class Versicolor:
    pass


def iris_factory(species):
    try:
        classname = species.capitalize()
        return globals()[classname]
    except KeyError:
        raise NotImplementedError


if __name__ == '__main__':
    iris = iris_factory('setosa')
    print(iris)
    # <class '__main__.Setosa'>

    iris = iris_factory('virginica')
    print(iris)
    # <class '__main__.Virginica'>

    iris = iris_factory('arctica')
    print(iris)
    # Traceback (most recent call last):
    # NotImplementedError
class PDF:
    pass

class TXT:
    pass


class File:
    def __new__(cls, *args, **kwargs):
        filename, extension = args[0].split('.')
        if extension == 'pdf':
            return PDF()
        elif extension == 'txt':
            return TXT()


if __name__ == '__main__':
    file = File('myfile.pdf')
    print(file)
    # <__main__.PDF object at 0x...>

    file = File('myfile.txt')
    print(file)
    # <__main__.TXT object at 0x...>
from abc import ABCMeta, abstractproperty


class Document(metaclass=ABCMeta):
    @abstractproperty
    @property
    def _extension(self):
        return

    def __new__(cls, filename, *args, **kwargs):
        name, extension = filename.split('.')
        for cls in Document.__subclasses__():
            if cls._extension == extension:
                return super().__new__(cls)
        else:
            raise NotImplementedError('File format unknown')


class PDF(Document):
    _extension = 'pdf'

class Txt(Document):
    _extension = 'txt'

class Word(Document):
    _extension = 'docx'


if __name__ == '__main__':
    file = Document('myfile.txt')
    print(type(file))
    # <class '__main__.Txt'>

    file = Document('myfile.pdf')
    print(type(file))
    # <class '__main__.PDF'>
from abc import ABCMeta, abstractproperty, abstractmethod
from dataclasses import dataclass


@dataclass
class ConfigParser(metaclass=ABCMeta):
    _filename: str

    @abstractproperty
    @property
    def _extension(self):
        pass

    def show(self):
        content = self.__read()
        return self._parse(content)

    @abstractmethod
    def _parse(self, content: str) -> dict:
        return NotImplementedError

    def __read(self):
        with open(self._filename) as file:
            return file.read()

    def __new__(cls, filename, *args, **kwargs):
        _, extension = filename.split('.')
        for parser in cls.__subclasses__():
            if parser._extension == extension:
                instance = super().__new__(parser)
                instance.__init__(filename)
                return instance
        else:
            raise NotImplementedError('Parser for given file type not found')


class ConfigParserINI(ConfigParser):
    _extension = 'ini'

    def _parse(self, content: str) -> dict:
        print('Parsing INI file')


class ConfigParserCSV(ConfigParser):
    _extension = 'csv'

    def _parse(self, content: str) -> dict:
        print('Parsing CSV file')


class ConfigParserYAML(ConfigParser):
    _extension = 'yaml'

    def _parse(self, content: str) -> dict:
        print('Parsing YAML file')


class ConfigFileJSON(ConfigParser):
    _extension = 'json'

    def _parse(self, content: str) -> dict:
        print('Parsing JSON file')


class ConfigFileXML(ConfigParser):
    _extension = 'xml'

    def _parse(self, content: str) -> dict:
        print('Parsing XML file')


if __name__ == '__main__':
    # iris.csv or *.csv, *.json *.yaml...
    # filename = input('Type filename: ')
    config = ConfigParser('/tmp/myfile.json')
    config.show()
import os


class HttpClientInterface:
    def GET(self):
        raise NotImplementedError

    def POST(self):
        raise NotImplementedError


class GatewayLive(HttpClientInterface):
    def GET(self):
        print('Execute GET request over network')
        return ...

    def POST(self):
        print('Execute POST request over network')
        return ...


class GatewayStub(HttpClientInterface):
    def GET(self):
        print('Returning stub GET')
        return {'firstname': 'Mark', 'lastname': 'Watney'}

    def POST(self):
        print('Returning stub POST')
        return {'status': 200, 'reason': 'OK'}


class HttpGatewayFactory:
    def __new__(cls, *args, **kwargs):
        if os.getenv('ENVIRONMENT') == 'production':
            return GatewayLive()
        else:
            return GatewayStub()


if __name__ == '__main__':
    os.environ['ENVIRONMENT'] = 'testing'

    client = HttpGatewayFactory()
    result = client.GET()
    # Returning stub GET
    result = client.POST()
    # Returning stub POST

    os.environ['ENVIRONMENT'] = 'production'

    client = HttpGatewayFactory()
    result = client.GET()
    # Execute GET request over network
    result = client.POST()
    # Execute POST request over network
from abc import ABCMeta, abstractmethod


class Path(metaclass=ABCMeta):
    def __new__(cls, path, *args, **kwargs):
        if path.startswith(r'C:\Users'):
            instance = object.__new__(WindowsPath)
        if path.startswith('/home'):
            return object.__new__(LinuxPath)
        if path.startswith('/Users'):
            return object.__new__(macOSPath)
        instance.__init__(path)
        return instance

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

    @abstractmethod
    def dir_create(self): pass

    @abstractmethod
    def dir_list(self): pass

    @abstractmethod
    def dir_remove(self): pass


class WindowsPath(Path):
    def dir_create(self):
        print('create directory on ')

    def dir_list(self):
        print('list directory on ')

    def dir_remove(self):
        print('remove directory on ')


class LinuxPath(Path):
    def dir_create(self):
        print('create directory on ')

    def dir_list(self):
        print('list directory on ')

    def dir_remove(self):
        print('remove directory on ')


class macOSPath(Path):
    def dir_create(self):
        print('create directory on ')

    def dir_list(self):
        print('list directory on ')

    def dir_remove(self):
        print('remove directory on ')


if __name__ == '__main__':
    file = Path(r'C:\Users\MWatney\myfile.txt')
    print(type(file))
    # <class '__main__.WindowsPath'>

    file = Path(r'/home/mwatney/myfile.txt')
    print(type(file))
    # <class '__main__.LinuxPath'>

    file = Path(r'/Users/mwatney/myfile.txt')
    print(type(file))
    # <class '__main__.macOSPath'>

9.3.5. Assignments

Code 9.17. Solution
"""
* Assignment: DesignPatterns Creational FactoryMethod
* Complexity: medium
* Lines of code: 8 lines
* Time: 8 min

English:
    1. Create `result: list[Iris]`
    2. Iterate over `DATA` skipping header
    3. Separate `features` from `species` in each row
    4. Append to `result`:
        a. if `species` is "setosa" append instance of a class `Setosa`
        b. if `species` is "versicolor" append instance of a class `Versicolor`
        c. if `species` is "virginica" append instance of a class `Virginica`
    5. Initialize instances with `features` using `*features` notation
    6. Run doctests - all must succeed

Polish:
    1. Stwórz `result: list[Iris]`
    2. Iterując po `DATA` pomiń nagłówek
    3. Odseparuj `features` od `species` w każdym wierszu
    4. Dodaj do `result`:
        a. jeżeli `species` to "setosa" to dodaj instancję klasy `Setosa`
        b. jeżeli `species` to "versicolor" to dodaj instancję klasy `Versicolor`
        c. jeżeli `species` to "virginica" to dodaj instancję klasy `Virginica`
    5. Instancje inicjalizuj danymi z `features` używając notacji `*features`
    6. Uruchom doctesty - wszystkie muszą się powieść

Hints:
    * `globals()[classname]`

Tests:
    >>> import sys; sys.tracebacklimit = 0

    >>> result  # doctest: +NORMALIZE_WHITESPACE
    [Virginica(5.8, 2.7, 5.1, 1.9),
     Setosa(5.1, 3.5, 1.4, 0.2),
     Versicolor(5.7, 2.8, 4.1, 1.3),
     Virginica(6.3, 2.9, 5.6, 1.8),
     Versicolor(6.4, 3.2, 4.5, 1.5),
     Setosa(4.7, 3.2, 1.3, 0.2)]
"""

from dataclasses import dataclass


DATA = [('Sepal length', 'Sepal width', 'Petal length', 'Petal width', 'Species'),
        (5.8, 2.7, 5.1, 1.9, 'virginica'),
        (5.1, 3.5, 1.4, 0.2, 'setosa'),
        (5.7, 2.8, 4.1, 1.3, 'versicolor'),
        (6.3, 2.9, 5.6, 1.8, 'virginica'),
        (6.4, 3.2, 4.5, 1.5, 'versicolor'),
        (4.7, 3.2, 1.3, 0.2, 'setosa')]


@dataclass(repr=False)
class Iris:
    _sepal_length: float
    _sepal_width: float
    _petal_length: float
    _petal_width: float

    def __repr__(self):
        name = self.__class__.__name__
        args = tuple(self.__dict__.values())
        return f'{name}{args}'


class Setosa(Iris):
    pass


class Versicolor(Iris):
    pass


class Virginica(Iris):
    pass


result: list