Общее

"""
*What is this pattern about?
In Java and other languages, the Abstract Factory Pattern serves to provide an interface for
creating related/dependent objects without need to specify their
actual class.
The idea is to abstract the creation of objects depending on business
logic, platform choice, etc.
In Python, the interface we use is simply a callable, which is "builtin" interface
in Python, and in normal circumstances we can simply use the class itself as
that callable, because classes are first class objects in Python.
*What does this example do?
This particular implementation abstracts the creation of a pet and
does so depending on the factory we chose (Dog or Cat, or random_animal)
This works because both Dog/Cat and random_animal respect a common
interface (callable for creation and .speak()).
Now my application can create pets abstractly and decide later,
based on my own criteria, dogs over cats.
*Where is the pattern used practically?
*References:
https://sourcemaking.com/design_patterns/abstract_factory
http://ginstrom.com/scribbles/2007/10/08/design-patterns-python-style/
*TL;DR
Provides a way to encapsulate a group of individual factories.
"""

import random


class PetShop:

    """A pet shop"""

    def __init__(self, animal_factory=None):
        """pet_factory is our abstract factory.  We can set it at will."""

        self.pet_factory = animal_factory

    def show_pet(self):
        """Creates and shows a pet using the abstract factory"""

        pet = self.pet_factory()
        print("We have a lovely {}".format(pet))
        print("It says {}".format(pet.speak()))


class Dog:
    def speak(self):
        return "woof"

    def __str__(self):
        return "Dog"


class Cat:
    def speak(self):
        return "meow"

    def __str__(self):
        return "Cat"


# Additional factories:

# Create a random animal
def random_animal():
    """Let's be dynamic!"""
    return random.choice([Dog, Cat])()


# Show pets with various factories
if __name__ == "__main__":

    # A Shop that sells only cats
    cat_shop = PetShop(Cat)
    cat_shop.show_pet()
    print("")

    # A shop that sells random animals
    shop = PetShop(random_animal)
    for i in range(3):
        shop.show_pet()
        print("=" * 20)

# OUTPUT #
# We have a lovely Cat
# It says meow
#
# We have a lovely Dog
# It says woof
# ====================
# We have a lovely Cat
# It says meow
# ====================
# We have a lovely Cat
# It says meow
# ====================

"""
*What is this pattern about?
It decouples the creation of a complex object and its representation,
so that the same process can be reused to build objects from the same
family.
This is useful when you must separate the specification of an object
from its actual representation (generally for abstraction).
*What does this example do?
The first example achieves this by using an abstract base
class for a building, where the initializer (__init__ method) specifies the
steps needed, and the concrete subclasses implement these steps.
In other programming languages, a more complex arrangement is sometimes
necessary. In particular, you cannot have polymorphic behaviour in a constructor in C++ -
see https://stackoverflow.com/questions/1453131/how-can-i-get-polymorphic-behavior-in-a-c-constructor
- which means this Python technique will not work. The polymorphism
required has to be provided by an external, already constructed
instance of a different class.
In general, in Python this won't be necessary, but a second example showing
this kind of arrangement is also included.
*Where is the pattern used practically?
*References:
https://sourcemaking.com/design_patterns/builder
*TL;DR
Decouples the creation of a complex object and its representation.
"""


# Abstract Building
class Building:
    def __init__(self):
        self.build_floor()
        self.build_size()

    def build_floor(self):
        raise NotImplementedError

    def build_size(self):
        raise NotImplementedError

    def __repr__(self):
        return 'Floor: {0.floor} | Size: {0.size}'.format(self)


# Concrete Buildings
class House(Building):
    def build_floor(self):
        self.floor = 'One'

    def build_size(self):
        self.size = 'Big'


class Flat(Building):
    def build_floor(self):
        self.floor = 'More than One'

    def build_size(self):
        self.size = 'Small'


# In some very complex cases, it might be desirable to pull out the building
# logic into another function (or a method on another class), rather than being
# in the base class '__init__'. (This leaves you in the strange situation where
# a concrete class does not have a useful constructor)


class ComplexBuilding:
    def __repr__(self):
        return 'Floor: {0.floor} | Size: {0.size}'.format(self)


class ComplexHouse(ComplexBuilding):
    def build_floor(self):
        self.floor = 'One'

    def build_size(self):
        self.size = 'Big and fancy'


def construct_building(cls):
    building = cls()
    building.build_floor()
    building.build_size()
    return building


def main():
    """
    >>> house = House()
    >>> house
    Floor: One | Size: Big
    >>> flat = Flat()
    >>> flat
    Floor: More than One | Size: Small
    # Using an external constructor function:
    >>> complex_house = construct_building(ComplexHouse)
    >>> complex_house
    Floor: One | Size: Big and fancy
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod()

"""*What is this pattern about?
A Factory is an object for creating other objects.
*What does this example do?
The code shows a way to localize words in two languages: English and
Greek. "get_localizer" is the factory function that constructs a
localizer depending on the language chosen. The localizer object will
be an instance from a different class according to the language
localized. However, the main code does not have to worry about which
localizer will be instantiated, since the method "localize" will be called
in the same way independently of the language.
*Where can the pattern be used practically?
The Factory Method can be seen in the popular web framework Django:
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.
*References:
http://ginstrom.com/scribbles/2007/10/08/design-patterns-python-style/
*TL;DR
Creates objects without having to specify the exact class.
"""


class GreekLocalizer:
    """A simple localizer a la gettext"""

    def __init__(self):
        self.translations = {"dog": "σκύλος", "cat": "γάτα"}

    def localize(self, msg):
        """We'll punt if we don't have a translation"""
        return self.translations.get(msg, msg)


class EnglishLocalizer:
    """Simply echoes the message"""

    def localize(self, msg):
        return msg


def get_localizer(language="English"):
    """Factory"""
    localizers = {
        "English": EnglishLocalizer,
        "Greek": GreekLocalizer,
    }
    return localizers[language]()


def main():
    """
    # Create our localizers
    >>> e, g = get_localizer(language="English"), get_localizer(language="Greek")
    # Localize some text
    >>> for msg in "dog parrot cat bear".split():
    ...     print(e.localize(msg), g.localize(msg))
    dog σκύλος
    parrot parrot
    cat γάτα
    bear bear
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod()

class Point:
    __slots__ = ('x', 'y',)

    def __init__(self, x, y):
        self.x = x
        self.y = y

# При таком классическом определении класса Point создать новую точку можно семью способами

def make_object(cls, *args, **kwargs):
    return cls(*args, **kwargs)

point1 = Point(1, 2)
point2 = eval('{}({}, {})'.format('Point', 2, 4)) # Опасно
point3 = getattr(sys.modules[__name__], 'Point')(3, 6)
point4 = globals()['Point'](4, 8)
point5 = make_object(Point, 5, 10)
point6 = copy.deepcopy(point5)
point6.x = 6
point6.y = 12
point7 = point1.__class__(7, 14)

"""
*What is this pattern about?
This patterns aims to reduce the number of classes required by an
application. Instead of relying on subclasses it creates objects by
copying a prototypical instance at run-time.
This is useful as it makes it easier to derive new kinds of objects,
when instances of the class have only a few different combinations of
state, and when instantiation is expensive.
*What does this example do?
When the number of prototypes in an application can vary, it can be
useful to keep a Dispatcher (aka, Registry or Manager). This allows
clients to query the Dispatcher for a prototype before cloning a new
instance.
Below provides an example of such Dispatcher, which contains three
copies of the prototype: 'default', 'objecta' and 'objectb'.
*TL;DR
Creates new object instances by cloning prototype.
"""


class Prototype:

    value = 'default'

    def clone(self, **attrs):
        """Clone a prototype and update inner attributes dictionary"""
        # Python in Practice, Mark Summerfield
        obj = self.__class__()
        obj.__dict__.update(attrs)
        return obj


class PrototypeDispatcher:
    def __init__(self):
        self._objects = {}

    def get_objects(self):
        """Get all objects"""
        return self._objects

    def register_object(self, name, obj):
        """Register an object"""
        self._objects[name] = obj

    def unregister_object(self, name):
        """Unregister an object"""
        del self._objects[name]


def main():
    """
    >>> dispatcher = PrototypeDispatcher()
    >>> prototype = Prototype()
    >>> d = prototype.clone()
    >>> a = prototype.clone(value='a-value', category='a')
    >>> b = prototype.clone(value='b-value', is_checked=True)
    >>> dispatcher.register_object('objecta', a)
    >>> dispatcher.register_object('objectb', b)
    >>> dispatcher.register_object('default', d)
    >>> [{n: p.value} for n, p in dispatcher.get_objects().items()]
    [{'objecta': 'a-value'}, {'objectb': 'b-value'}, {'default': 'default'}]
    """


if __name__ == '__main__':
    import doctest
    doctest.testmod()

"""
Yet one singleton realization on Python without metaclass. Singleton may has __init__ method which will call only when first object create.
http://code.activestate.com/recipes/577208-singletonsubclass-with-once-initialization/
"""


class Singleton(object):

    def __new__(cls,*dt,**mp):
        if not hasattr(cls,'_inst'):
            cls._inst = super(Singleton, cls).__new__(cls,dt,mp)
        else:
            def init_pass(self,*dt,**mp):pass
            cls.__init__ = init_pass

        return cls._inst

if __name__ == '__main__':


    class A(Singleton):

        def __init__(self):
            """Super constructor
                There is we can open file or create connection to the database
            """
            print "A init"


    a1 = A()
    a2 = A()

"""
*What is this pattern about?
The Borg pattern (also known as the Monostate pattern) is a way to
implement singleton behavior, but instead of having only one instance
of a class, there are multiple instances that share the same state. In
other words, the focus is on sharing state instead of sharing instance
identity.
*What does this example do?
To understand the implementation of this pattern in Python, it is
important to know that, in Python, instance attributes are stored in a
attribute dictionary called __dict__. Usually, each instance will have
its own dictionary, but the Borg pattern modifies this so that all
instances have the same dictionary.
In this example, the __shared_state attribute will be the dictionary
shared between all instances, and this is ensured by assigining
__shared_state to the __dict__ variable when initializing a new
instance (i.e., in the __init__ method). Other attributes are usually
added to the instance's attribute dictionary, but, since the attribute
dictionary itself is shared (which is __shared_state), all other
attributes will also be shared.
*Where is the pattern used practically?
Sharing state is useful in applications like managing database connections:
https://github.com/onetwopunch/pythonDbTemplate/blob/master/database.py
*References:
https://fkromer.github.io/python-pattern-references/design/#singleton
*TL;DR
Provides singleton-like behavior sharing state between instances.
"""


class Borg:
    __shared_state = {}

    def __init__(self):
        self.__dict__ = self.__shared_state
        self.state = 'Init'

    def __str__(self):
        return self.state


class YourBorg(Borg):
    pass


def main():
    """
    >>> rm1 = Borg()
    >>> rm2 = Borg()
    >>> rm1.state = 'Idle'
    >>> rm2.state = 'Running'
    >>> print('rm1: {0}'.format(rm1))
    rm1: Running
    >>> print('rm2: {0}'.format(rm2))
    rm2: Running
    # When the `state` attribute is modified from instance `rm2`,
    # the value of `state` in instance `rm1` also changes
    >>> rm2.state = 'Zombie'
    >>> print('rm1: {0}'.format(rm1))
    rm1: Zombie
    >>> print('rm2: {0}'.format(rm2))
    rm2: Zombie
    # Even though `rm1` and `rm2` share attributes, the instances are not the same
    >>> rm1 is rm2
    False
    # Shared state is also modified from a subclass instance `rm3`
    >>> rm3 = YourBorg()
    >>> print('rm1: {0}'.format(rm1))
    rm1: Init
    >>> print('rm2: {0}'.format(rm2))
    rm2: Init
    >>> print('rm3: {0}'.format(rm3))
    rm3: Init
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod()

#!/usr/bin/env python3
# Copyright © 2012-13 Qtrac Ltd. All rights reserved.
# This program or module is free software: you can redistribute it
# and/or modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version. It is provided for
# educational purposes and is distributed in the hope that it will be
# useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.

import re
import urllib.request


_URL = "http://www.bankofcanada.ca/stats/assets/csv/fx-seven-day.csv"


def get(refresh=False):
    if refresh:
        get.rates = {}
    if get.rates:
        return get.rates
    with urllib.request.urlopen(_URL) as file:
        for line in file:
            line = line.rstrip().decode("utf-8")
            if not line or line.startswith(("#", "Date")):
                continue
            name, currency, *rest = re.split(r"/s*,/s*", line)
            key = "{} ({})".format(name, currency)
            try:
                get.rates[key] = float(rest[-1])
            except ValueError as err:
                print("error {}: {}".format(err, line))
    return get.rates
get.rates = {}


if __name__ == "__main__":
    import sys
    if sys.stdout.isatty():
        print(get())
    else:
        print("Loaded OK")

"""
*What is this pattern about?
The Adapter pattern provides a different interface for a class. We can
think about it as a cable adapter that allows you to charge a phone
somewhere that has outlets in a different shape. Following this idea,
the Adapter pattern is useful to integrate classes that couldn't be
integrated due to their incompatible interfaces.
*What does this example do?
The example has classes that represent entities (Dog, Cat, Human, Car)
that make different noises. The Adapter class provides a different
interface to the original methods that make such noises. So the
original interfaces (e.g., bark and meow) are available under a
different name: make_noise.
*Where is the pattern used practically?
The Grok framework uses adapters to make objects work with a
particular API without modifying the objects themselves:
http://grok.zope.org/doc/current/grok_overview.html#adapters
*References:
http://ginstrom.com/scribbles/2008/11/06/generic-adapter-class-in-python/
https://sourcemaking.com/design_patterns/adapter
http://python-3-patterns-idioms-test.readthedocs.io/en/latest/ChangeInterface.html#adapter
*TL;DR
Allows the interface of an existing class to be used as another interface.
"""


class Dog:
    def __init__(self):
        self.name = "Dog"

    def bark(self):
        return "woof!"


class Cat:
    def __init__(self):
        self.name = "Cat"

    def meow(self):
        return "meow!"


class Human:
    def __init__(self):
        self.name = "Human"

    def speak(self):
        return "'hello'"


class Car:
    def __init__(self):
        self.name = "Car"

    def make_noise(self, octane_level):
        return "vroom{0}".format("!" * octane_level)


class Adapter:
    """
    Adapts an object by replacing methods.
    Usage:
    dog = Dog()
    dog = Adapter(dog, make_noise=dog.bark)
    """

    def __init__(self, obj, **adapted_methods):
        """We set the adapted methods in the object's dict"""
        self.obj = obj
        self.__dict__.update(adapted_methods)

    def __getattr__(self, attr):
        """All non-adapted calls are passed to the object"""
        return getattr(self.obj, attr)

    def original_dict(self):
        """Print original object dict"""
        return self.obj.__dict__


def main():
    """
    >>> objects = []
    >>> dog = Dog()
    >>> print(dog.__dict__)
    {'name': 'Dog'}
    >>> objects.append(Adapter(dog, make_noise=dog.bark))
    >>> objects[0].__dict__['obj'], objects[0].__dict__['make_noise']
    (<...Dog object at 0x...>, <bound method Dog.bark of <...Dog object at 0x...>>)
    >>> print(objects[0].original_dict())
    {'name': 'Dog'}
    >>> cat = Cat()
    >>> objects.append(Adapter(cat, make_noise=cat.meow))
    >>> human = Human()
    >>> objects.append(Adapter(human, make_noise=human.speak))
    >>> car = Car()
    >>> objects.append(Adapter(car, make_noise=lambda: car.make_noise(3)))
    >>> for obj in objects:
    ...    print("A {0} goes {1}".format(obj.name, obj.make_noise()))
    A Dog goes woof!
    A Cat goes meow!
    A Human goes 'hello'
    A Car goes vroom!!!
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod(optionflags=doctest.ELLIPSIS)

"""
*References:
http://en.wikibooks.org/wiki/Computer_Science_Design_Patterns/Bridge_Pattern#Python
*TL;DR
Decouples an abstraction from its implementation.
"""


# ConcreteImplementor 1/2
class DrawingAPI1:
    def draw_circle(self, x, y, radius):
        print('API1.circle at {}:{} radius {}'.format(x, y, radius))


# ConcreteImplementor 2/2
class DrawingAPI2:
    def draw_circle(self, x, y, radius):
        print('API2.circle at {}:{} radius {}'.format(x, y, radius))


# Refined Abstraction
class CircleShape:
    def __init__(self, x, y, radius, drawing_api):
        self._x = x
        self._y = y
        self._radius = radius
        self._drawing_api = drawing_api

    # low-level i.e. Implementation specific
    def draw(self):
        self._drawing_api.draw_circle(self._x, self._y, self._radius)

    # high-level i.e. Abstraction specific
    def scale(self, pct):
        self._radius *= pct


def main():
    """
    >>> shapes = (CircleShape(1, 2, 3, DrawingAPI1()), CircleShape(5, 7, 11, DrawingAPI2()))
    >>> for shape in shapes:
    ...    shape.scale(2.5)
    ...    shape.draw()
    API1.circle at 1:2 radius 7.5
    API2.circle at 5:7 radius 27.5
    """


if __name__ == '__main__':
    import doctest
    doctest.testmod()

"""
*What is this pattern about?
The composite pattern describes a group of objects that is treated the
same way as a single instance of the same type of object. The intent of
a composite is to "compose" objects into tree structures to represent
part-whole hierarchies. Implementing the composite pattern lets clients
treat individual objects and compositions uniformly.
*What does this example do?
The example implements a graphic class，which can be either an ellipse
or a composition of several graphics. Every graphic can be printed.
*Where is the pattern used practically?
In graphics editors a shape can be basic or complex. An example of a
simple shape is a line, where a complex shape is a rectangle which is
made of four line objects. Since shapes have many operations in common
such as rendering the shape to screen, and since shapes follow a
part-whole hierarchy, composite pattern can be used to enable the
program to deal with all shapes uniformly.
*References:
https://en.wikipedia.org/wiki/Composite_pattern
https://infinitescript.com/2014/10/the-23-gang-of-three-design-patterns/
*TL;DR
Describes a group of objects that is treated as a single instance.
"""


class Graphic:
    def render(self):
        raise NotImplementedError("You should implement this.")


class CompositeGraphic(Graphic):
    def __init__(self):
        self.graphics = []

    def render(self):
        for graphic in self.graphics:
            graphic.render()

    def add(self, graphic):
        self.graphics.append(graphic)

    def remove(self, graphic):
        self.graphics.remove(graphic)


class Ellipse(Graphic):
    def __init__(self, name):
        self.name = name

    def render(self):
        print("Ellipse: {}".format(self.name))


if __name__ == '__main__':
    ellipse1 = Ellipse("1")
    ellipse2 = Ellipse("2")
    ellipse3 = Ellipse("3")
    ellipse4 = Ellipse("4")

    graphic1 = CompositeGraphic()
    graphic2 = CompositeGraphic()

    graphic1.add(ellipse1)
    graphic1.add(ellipse2)
    graphic1.add(ellipse3)
    graphic2.add(ellipse4)

    graphic = CompositeGraphic()

    graphic.add(graphic1)
    graphic.add(graphic2)

    graphic.render()

# OUTPUT #
# Ellipse: 1
# Ellipse: 2
# Ellipse: 3
# Ellipse: 4

"""
*What is this pattern about?
The Decorator pattern is used to dynamically add a new feature to an
object without changing its implementation. It differs from
inheritance because the new feature is added only to that particular
object, not to the entire subclass.
*What does this example do?
This example shows a way to add formatting options (boldface and
italic) to a text by appending the corresponding tags (<b> and
<i>). Also, we can see that decorators can be applied one after the other,
since the original text is passed to the bold wrapper, which in turn
is passed to the italic wrapper.
*Where is the pattern used practically?
The Grok framework uses decorators to add functionalities to methods,
like permissions or subscription to an event:
http://grok.zope.org/doc/current/reference/decorators.html
*References:
https://sourcemaking.com/design_patterns/decorator
*TL;DR
Adds behaviour to object without affecting its class.
"""


class TextTag:
    """Represents a base text tag"""

    def __init__(self, text):
        self._text = text

    def render(self):
        return self._text


class BoldWrapper(TextTag):
    """Wraps a tag in <b>"""

    def __init__(self, wrapped):
        self._wrapped = wrapped

    def render(self):
        return "<b>{}</b>".format(self._wrapped.render())


class ItalicWrapper(TextTag):
    """Wraps a tag in <i>"""

    def __init__(self, wrapped):
        self._wrapped = wrapped

    def render(self):
        return "<i>{}</i>".format(self._wrapped.render())


if __name__ == '__main__':
    simple_hello = TextTag("hello, world!")
    special_hello = ItalicWrapper(BoldWrapper(simple_hello))
    print("before:", simple_hello.render())
    print("after:", special_hello.render())

# OUTPUT #
# before: hello, world!
# after: <i><b>hello, world!</b></i>

"""
Example from https://en.wikipedia.org/wiki/Facade_pattern#Python
*What is this pattern about?
The Facade pattern is a way to provide a simpler unified interface to
a more complex system. It provides an easier way to access functions
of the underlying system by providing a single entry point.
This kind of abstraction is seen in many real life situations. For
example, we can turn on a computer by just pressing a button, but in
fact there are many procedures and operations done when that happens
(e.g., loading programs from disk to memory). In this case, the button
serves as an unified interface to all the underlying procedures to
turn on a computer.
*Where is the pattern used practically?
This pattern can be seen in the Python standard library when we use
the isdir function. Although a user simply uses this function to know
whether a path refers to a directory, the system makes a few
operations and calls other modules (e.g., os.stat) to give the result.
*References:
https://sourcemaking.com/design_patterns/facade
https://fkromer.github.io/python-pattern-references/design/#facade
http://python-3-patterns-idioms-test.readthedocs.io/en/latest/ChangeInterface.html#facade
*TL;DR
Provides a simpler unified interface to a complex system.
"""


# Complex computer parts
class CPU:
    """
    Simple CPU representation.
    """
    def freeze(self):
        print("Freezing processor.")

    def jump(self, position):
        print("Jumping to:", position)

    def execute(self):
        print("Executing.")


class Memory:
    """
    Simple memory representation.
    """
    def load(self, position, data):
        print("Loading from {0} data: '{1}'.".format(position, data))


class SolidStateDrive:
    """
    Simple solid state drive representation.
    """
    def read(self, lba, size):
        return "Some data from sector {0} with size {1}".format(lba, size)


class ComputerFacade:
    """
    Represents a facade for various computer parts.
    """
    def __init__(self):
        self.cpu = CPU()
        self.memory = Memory()
        self.ssd = SolidStateDrive()

    def start(self):
        self.cpu.freeze()
        self.memory.load("0x00", self.ssd.read("100", "1024"))
        self.cpu.jump("0x00")
        self.cpu.execute()


def main():
    """
    >>> computer_facade = ComputerFacade()
    >>> computer_facade.start()
    Freezing processor.
    Loading from 0x00 data: 'Some data from sector 100 with size 1024'.
    Jumping to: 0x00
    Executing.
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod(optionflags=doctest.ELLIPSIS)

red, green, blue = 'red', 'green', 'blue'
x = (red, green, blue, red, green, blue, green)

"""
*What is this pattern about?
This pattern aims to minimise the number of objects that are needed by
a program at run-time. A Flyweight is an object shared by multiple
contexts, and is indistinguishable from an object that is not shared.
The state of a Flyweight should not be affected by it's context, this
is known as its intrinsic state. The decoupling of the objects state
from the object's context, allows the Flyweight to be shared.
*What does this example do?
The example below sets-up an 'object pool' which stores initialised
objects. When a 'Card' is created it first checks to see if it already
exists instead of creating a new one. This aims to reduce the number of
objects initialised by the program.
*References:
http://codesnipers.com/?q=python-flyweights
https://python-patterns.guide/gang-of-four/flyweight/
*Examples in Python ecosystem:
https://docs.python.org/3/library/sys.html#sys.intern
*TL;DR
Minimizes memory usage by sharing data with other similar objects.
"""

import weakref


class Card:
    """The Flyweight"""

    # Could be a simple dict.
    # With WeakValueDictionary garbage collection can reclaim the object
    # when there are no other references to it.
    _pool = weakref.WeakValueDictionary()

    def __new__(cls, value, suit):
        # If the object exists in the pool - just return it
        obj = cls._pool.get(value + suit)
        # otherwise - create new one (and add it to the pool)
        if obj is None:
            obj = object.__new__(Card)
            cls._pool[value + suit] = obj
            # This row does the part we usually see in `__init__`
            obj.value, obj.suit = value, suit
        return obj

    # If you uncomment `__init__` and comment-out `__new__` -
    #   Card becomes normal (non-flyweight).
    # def __init__(self, value, suit):
    #     self.value, self.suit = value, suit

    def __repr__(self):
        return "<Card: {}{}>".format(self.value, self.suit)


def main():
    """
    >>> c1 = Card('9', 'h')
    >>> c2 = Card('9', 'h')
    >>> c1, c2
    (<Card: 9h>, <Card: 9h>)
    >>> c1 == c2
    True
    >>> c1 is c2
    True
    >>> c1.new_attr = 'temp'
    >>> c3 = Card('9', 'h')
    >>> hasattr(c3, 'new_attr')
    True
    >>> Card._pool.clear()
    >>> c4 = Card('9', 'h')
    >>> hasattr(c4, 'new_attr')
    False
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod()

"""
*TL;DR
Provides an interface to resource that is expensive to duplicate.
"""

import time


class SalesManager:
    def talk(self):
        print("Sales Manager ready to talk")


class Proxy:
    def __init__(self):
        self.busy = 'No'
        self.sales = None

    def talk(self):
        print("Proxy checking for Sales Manager availability")
        if self.busy == 'No':
            self.sales = SalesManager()
            time.sleep(0.1)
            self.sales.talk()
        else:
            time.sleep(0.1)
            print("Sales Manager is busy")


class NoTalkProxy(Proxy):
    def talk(self):
        print("Proxy checking for Sales Manager availability")
        time.sleep(0.1)
        print("This Sales Manager will not talk to you", "whether he/she is busy or not")


if __name__ == '__main__':
    p = Proxy()
    p.talk()
    p.busy = 'Yes'
    p.talk()
    p = NoTalkProxy()
    p.talk()
    p.busy = 'Yes'
    p.talk()

# OUTPUT #
# Proxy checking for Sales Manager availability
# Sales Manager ready to talk
# Proxy checking for Sales Manager availability
# Sales Manager is busy
# Proxy checking for Sales Manager availability
# This Sales Manager will not talk to you whether he/she is busy or not
# Proxy checking for Sales Manager availability
# This Sales Manager will not talk to you whether he/she is busy or not

"""
*What is this pattern about?
The Chain of responsibility is an object oriented version of the
`if ... elif ... elif ... else ...` idiom, with the
benefit that the condition–action blocks can be dynamically rearranged
and reconfigured at runtime.
This pattern aims to decouple the senders of a request from its
receivers by allowing request to move through chained
receivers until it is handled.
Request receiver in simple form keeps a reference to a single successor.
As a variation some receivers may be capable of sending requests out
in several directions, forming a `tree of responsibility`.
*TL;DR
Allow a request to pass down a chain of receivers until it is handled.
"""

import abc


class Handler(metaclass=abc.ABCMeta):

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

    def handle(self, request):
        """
        Handle request and stop.
        If can't - call next handler in chain.
        As an alternative you might even in case of success
        call the next handler.
        """
        res = self.check_range(request)
        if not res and self.successor:
            self.successor.handle(request)

    @abc.abstractmethod
    def check_range(self, request):
        """Compare passed value to predefined interval"""


class ConcreteHandler0(Handler):
    """Each handler can be different.
    Be simple and static...
    """

    @staticmethod
    def check_range(request):
        if 0 <= request < 10:
            print("request {} handled in handler 0".format(request))
            return True


class ConcreteHandler1(Handler):
    """... With it's own internal state"""

    start, end = 10, 20

    def check_range(self, request):
        if self.start <= request < self.end:
            print("request {} handled in handler 1".format(request))
            return True


class ConcreteHandler2(Handler):
    """... With helper methods."""

    def check_range(self, request):
        start, end = self.get_interval_from_db()
        if start <= request < end:
            print("request {} handled in handler 2".format(request))
            return True

    @staticmethod
    def get_interval_from_db():
        return (20, 30)


class FallbackHandler(Handler):
    @staticmethod
    def check_range(request):
        print("end of chain, no handler for {}".format(request))
        return False


def main():
    """
    >>> h0 = ConcreteHandler0()
    >>> h1 = ConcreteHandler1()
    >>> h2 = ConcreteHandler2(FallbackHandler())
    >>> h0.successor = h1
    >>> h1.successor = h2
    >>> requests = [2, 5, 14, 22, 18, 3, 35, 27, 20]
    >>> for request in requests:
    ...     h0.handle(request)
    request 2 handled in handler 0
    request 5 handled in handler 0
    request 14 handled in handler 1
    request 22 handled in handler 2
    request 18 handled in handler 1
    request 3 handled in handler 0
    end of chain, no handler for 35
    request 27 handled in handler 2
    request 20 handled in handler 2
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod(optionflags=doctest.ELLIPSIS)

"""
*TL;DR
Encapsulates all information needed to perform an action or trigger an event.
*Examples in Python ecosystem:
Django HttpRequest (without `execute` method):
 https://docs.djangoproject.com/en/2.1/ref/request-response/#httprequest-objects
"""

import os


class MoveFileCommand:
    def __init__(self, src, dest):
        self.src = src
        self.dest = dest

    def execute(self):
        self.rename(self.src, self.dest)

    def undo(self):
        self.rename(self.dest, self.src)

    def rename(self, src, dest):
        print("renaming {} to {}".format(src, dest))
        os.rename(src, dest)


def main():
    """
    >>> from os.path import lexists
    >>> command_stack = [
    ...     MoveFileCommand('foo.txt', 'bar.txt'),
    ...     MoveFileCommand('bar.txt', 'baz.txt')
    ... ]
    # Verify that none of the target files exist
    >>> assert not lexists("foo.txt")
    >>> assert not lexists("bar.txt")
    >>> assert not lexists("baz.txt")
    # Create empty file
    >>> open("foo.txt", "w").close()
    # Commands can be executed later on
    >>> for cmd in command_stack:
    ...     cmd.execute()
    renaming foo.txt to bar.txt
    renaming bar.txt to baz.txt
    # And can also be undone at will
    >>> for cmd in reversed(command_stack):
    ...     cmd.undo()
    renaming baz.txt to bar.txt
    renaming bar.txt to foo.txt
    >>> os.unlink("foo.txt")
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod()

"""
Интерпретатор (Interpreter) - паттерн поведения классов.
Для заданного языка определяет представление его грамматики,
а также интерпретатор предложений этого языка.
"""


class RomanNumeralInterpreter(object):
    """Интерпретатор римских цифр"""
    def __init__(self):
        self.grammar = {
            'I': 1,
            'V': 5,
            'X': 10,
            'L': 50,
            'C': 100,
            'D': 500,
            'M': 1000
        }

    def interpret(self, text):
        numbers = map(self.grammar.get, text)  # строки в значения
        if None in numbers:
            raise ValueError('Ошибочное значение: %s' % text)
        result = 0  # накапливаем результат
        temp = None  # запоминаем последнее значение
        while numbers:
            num = numbers.pop(0)
            if temp is None or temp >= num:
                result += num
            else:
                result += (num - temp * 2)
            temp = num
        return result


interp = RomanNumeralInterpreter()
print interp.interpret('MMMCMXCIX') == 3999  # True
print interp.interpret('MCMLXXXVIII') == 1988  # True

#!/usr/bin/env python3
# Copyright © 2012-13 Qtrac Ltd. All rights reserved.
# This program or module is free software: you can redistribute it and/or
# modify it under the terms of the GNU General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version. It is provided for educational
# purposes and is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.


class Bag:

    def __init__(self, items=None):
        self.__bag = {}
        if items is not None:
            for item in items:
                self.add(item)


    def clear(self):
        self.__bag.clear()


    def add(self, item):
        self.__bag[item] = self.__bag.get(item, 0) + 1


    def __delitem__(self, item):
        if self.__bag.get(item) is not None:
            self.__bag[item] -= 1
            if self.__bag[item] <= 0:
                del self.__bag[item]
        else:
            raise KeyError(str(item))


    def count(self, item):
        return self.__bag.get(item, 0)


    def __len__(self):
        return sum(count for count in self.__bag.values())


    def __iter__(self):
        return (item for item, count in self.__bag.items()
                for _ in range(count))


    items = __iter__


    def __contains__(self, item):
        return item in self.__bag

"""
https://www.djangospin.com/design-patterns-python/mediator/
Objects in a system communicate through a Mediator instead of directly with each other.
This reduces the dependencies between communicating objects, thereby reducing coupling.
*TL;DR
Encapsulates how a set of objects interact.
"""


class ChatRoom:
    """Mediator class"""

    def display_message(self, user, message):
        print("[{} says]: {}".format(user, message))


class User:
    """A class whose instances want to interact with each other"""

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

    def say(self, message):
        self.chat_room.display_message(self, message)

    def __str__(self):
        return self.name


def main():
    """
    >>> molly = User('Molly')
    >>> mark = User('Mark')
    >>> ethan = User('Ethan')
    >>> molly.say("Hi Team! Meeting at 3 PM today.")
    [Molly says]: Hi Team! Meeting at 3 PM today.
    >>> mark.say("Roger that!")
    [Mark says]: Roger that!
    >>> ethan.say("Alright.")
    [Ethan says]: Alright.
    """


if __name__ == '__main__':
    import doctest
    doctest.testmod()

#!/usr/bin/env python3
# Copyright © 2012-13 Qtrac Ltd. All rights reserved.
# This program or module is free software: you can redistribute it
# and/or modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version. It is provided for
# educational purposes and is distributed in the hope that it will be
# useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.

import collections


def main():
    form = Form()
    test_user_interaction_with(form)


class Form:

    def __init__(self):
        self.create_widgets()
        self.create_mediator()


    def create_widgets(self):
        self.nameText = Text()
        self.emailText = Text()
        self.okButton = Button("OK")
        self.cancelButton = Button("Cancel")


    def create_mediator(self):
        self.mediator = Mediator(((self.nameText, self.update_ui),
                (self.emailText, self.update_ui),
                (self.okButton, self.clicked),
                (self.cancelButton, self.clicked)))
        self.update_ui()


    def update_ui(self, widget=None):
        self.okButton.enabled = (bool(self.nameText.text) and
                                 bool(self.emailText.text))


    def clicked(self, widget):
        if widget == self.okButton:
            print("OK")
        elif widget == self.cancelButton:
            print("Cancel")


class Mediator:

    def __init__(self, widgetCallablePairs):
        self.callablesForWidget = collections.defaultdict(list)
        for widget, caller in widgetCallablePairs:
            self.callablesForWidget[widget].append(caller)
            widget.mediator = self


    def on_change(self, widget):
        callables = self.callablesForWidget.get(widget)
        if callables is not None:
            for caller in callables:
                caller(widget)
        else:
            raise AttributeError("No on_change() method registered for {}"
                    .format(widget))


class Mediated:

    def __init__(self):
        self.mediator = None


    def on_change(self):
        if self.mediator is not None:
            self.mediator.on_change(self)


class Button(Mediated):

    def __init__(self, text=""):
        super().__init__()
        self.enabled = True
        self.text = text


    def click(self):
        if self.enabled:
            self.on_change()


    def __str__(self):
        return "Button({!r}) {}".format(self.text,
                "enabled" if self.enabled else "disabled")


class Text(Mediated):

    def __init__(self, text=""):
        super().__init__()
        self.__text = text


    @property
    def text(self):
        return self.__text


    @text.setter
    def text(self, text):
        if self.text != text:
            self.__text = text
            self.on_change()


    def __str__(self):
        return "Text({!r})".format(self.text)


def test_user_interaction_with(form):
    form.okButton.click()           # Ignored because it is disabled
    print(form.okButton.enabled)    # False
    form.nameText.text = "Fred"
    print(form.okButton.enabled)    # False
    form.emailText.text = "fred@bloggers.com"
    print(form.okButton.enabled)    # True
    form.okButton.click()           # OK
    form.emailText.text = ""
    print(form.okButton.enabled)    # False
    form.cancelButton.click()       # Cancel


if __name__ == "__main__":
    main()

"""
http://code.activestate.com/recipes/413838-memento-closure/
*TL;DR
Provides the ability to restore an object to its previous state.
"""

from copy import copy
from copy import deepcopy


def memento(obj, deep=False):
    state = deepcopy(obj.__dict__) if deep else copy(obj.__dict__)

    def restore():
        obj.__dict__.clear()
        obj.__dict__.update(state)

    return restore


class Transaction:
    """A transaction guard.
    This is, in fact, just syntactic sugar around a memento closure.
    """

    deep = False
    states = []

    def __init__(self, deep, *targets):
        self.deep = deep
        self.targets = targets
        self.commit()

    def commit(self):
        self.states = [memento(target, self.deep) for target in self.targets]

    def rollback(self):
        for a_state in self.states:
            a_state()


class Transactional:
    """Adds transactional semantics to methods. Methods decorated  with
    @Transactional will rollback to entry-state upon exceptions.
    """

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

    def __get__(self, obj, T):
        def transaction(*args, **kwargs):
            state = memento(obj)
            try:
                return self.method(obj, *args, **kwargs)
            except Exception as e:
                state()
                raise e

        return transaction


class NumObj:
    def __init__(self, value):
        self.value = value

    def __repr__(self):
        return '<%s: %r>' % (self.__class__.__name__, self.value)

    def increment(self):
        self.value += 1

    @Transactional
    def do_stuff(self):
        self.value = '1111'  # <- invalid value
        self.increment()  # <- will fail and rollback


def main():
    """
    >>> num_obj = NumObj(-1)
    >>> print(num_obj)
    <NumObj: -1>
    >>> a_transaction = Transaction(True, num_obj)
    >>> try:
    ...    for i in range(3):
    ...        num_obj.increment()
    ...        print(num_obj)
    ...    a_transaction.commit()
    ...    print('-- committed')
    ...    for i in range(3):
    ...        num_obj.increment()
    ...        print(num_obj)
    ...    num_obj.value += 'x'  # will fail
    ...    print(num_obj)
    ... except Exception:
    ...    a_transaction.rollback()
    ...    print('-- rolled back')
    <NumObj: 0>
    <NumObj: 1>
    <NumObj: 2>
    -- committed
    <NumObj: 3>
    <NumObj: 4>
    <NumObj: 5>
    -- rolled back
    >>> print(num_obj)
    <NumObj: 2>
    >>> print('-- now doing stuff ...')
    -- now doing stuff ...
    >>> try:
    ...    num_obj.do_stuff()
    ... except Exception:
    ...    print('-> doing stuff failed!')
    ...    import sys
    ...    import traceback
    ...    traceback.print_exc(file=sys.stdout)
    -> doing stuff failed!
    Traceback (most recent call last):
    ...
    TypeError: ...str...int...
    >>> print(num_obj)
    <NumObj: 2>
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod(optionflags=doctest.ELLIPSIS)

"""
http://code.activestate.com/recipes/131499-observer-pattern/
*TL;DR
Maintains a list of dependents and notifies them of any state changes.
*Examples in Python ecosystem:
Django Signals: https://docs.djangoproject.com/en/2.1/topics/signals/
Flask Signals: http://flask.pocoo.org/docs/1.0/signals/
"""


class Subject:
    def __init__(self):
        self._observers = []

    def attach(self, observer):
        if observer not in self._observers:
            self._observers.append(observer)

    def detach(self, observer):
        try:
            self._observers.remove(observer)
        except ValueError:
            pass

    def notify(self, modifier=None):
        for observer in self._observers:
            if modifier != observer:
                observer.update(self)


class Data(Subject):
    def __init__(self, name=''):
        Subject.__init__(self)
        self.name = name
        self._data = 0

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

    @data.setter
    def data(self, value):
        self._data = value
        self.notify()


class HexViewer:
    def update(self, subject):
        print('HexViewer: Subject {} has data 0x{:x}'.format(subject.name, subject.data))


class DecimalViewer:
    def update(self, subject):
        print('DecimalViewer: Subject %s has data %d' % (subject.name, subject.data))


def main():
    """
    >>> data1 = Data('Data 1')
    >>> data2 = Data('Data 2')
    >>> view1 = DecimalViewer()
    >>> view2 = HexViewer()
    >>> data1.attach(view1)
    >>> data1.attach(view2)
    >>> data2.attach(view2)
    >>> data2.attach(view1)
    >>> data1.data = 10
    DecimalViewer: Subject Data 1 has data 10
    HexViewer: Subject Data 1 has data 0xa
    >>> data2.data = 15
    HexViewer: Subject Data 2 has data 0xf
    DecimalViewer: Subject Data 2 has data 15
    >>> data1.data = 3
    DecimalViewer: Subject Data 1 has data 3
    HexViewer: Subject Data 1 has data 0x3
    >>> data2.data = 5
    HexViewer: Subject Data 2 has data 0x5
    DecimalViewer: Subject Data 2 has data 5
    # Detach HexViewer from data1 and data2
    >>> data1.detach(view2)
    >>> data2.detach(view2)
    >>> data1.data = 10
    DecimalViewer: Subject Data 1 has data 10
    >>> data2.data = 15
    DecimalViewer: Subject Data 2 has data 15
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod()

"""
Implementation of the state pattern
http://ginstrom.com/scribbles/2007/10/08/design-patterns-python-style/
*TL;DR
Implements state as a derived class of the state pattern interface.
Implements state transitions by invoking methods from the pattern's superclass.
"""


class State:

    """Base state. This is to share functionality"""

    def scan(self):
        """Scan the dial to the next station"""
        self.pos += 1
        if self.pos == len(self.stations):
            self.pos = 0
        print("Scanning... Station is {} {}".format(self.stations[self.pos], self.name))


class AmState(State):
    def __init__(self, radio):
        self.radio = radio
        self.stations = ["1250", "1380", "1510"]
        self.pos = 0
        self.name = "AM"

    def toggle_amfm(self):
        print("Switching to FM")
        self.radio.state = self.radio.fmstate


class FmState(State):
    def __init__(self, radio):
        self.radio = radio
        self.stations = ["81.3", "89.1", "103.9"]
        self.pos = 0
        self.name = "FM"

    def toggle_amfm(self):
        print("Switching to AM")
        self.radio.state = self.radio.amstate


class Radio:

    """A radio. It has a scan button, and an AM/FM toggle switch."""

    def __init__(self):
        """We have an AM state and an FM state"""
        self.amstate = AmState(self)
        self.fmstate = FmState(self)
        self.state = self.amstate

    def toggle_amfm(self):
        self.state.toggle_amfm()

    def scan(self):
        self.state.scan()


def main():
    """
    >>> radio = Radio()
    >>> actions = [radio.scan] * 2 + [radio.toggle_amfm] + [radio.scan] * 2
    >>> actions *= 2
    >>> for action in actions:
    ...    action()
    Scanning... Station is 1380 AM
    Scanning... Station is 1510 AM
    Switching to FM
    Scanning... Station is 89.1 FM
    Scanning... Station is 103.9 FM
    Scanning... Station is 81.3 FM
    Scanning... Station is 89.1 FM
    Switching to AM
    Scanning... Station is 1250 AM
    Scanning... Station is 1380 AM
    """


if __name__ == '__main__':
    import doctest
    doctest.testmod()

"""
Состояние (State) - паттерн поведения объектов.
Позволяет объекту варьировать свое поведение в зависимости от внутреннего состояния.
Извне создается впечатление, что изменился класс объекта.
"""


class LampStateBase(object):
    """Состояние лампы"""
    def get_color(self):
        raise NotImplementedError()


class GreenLampState(LampStateBase):
    def get_color(self):
        return 'Green'


class RedLampState(LampStateBase):
    def get_color(self):
        return 'Red'


class BlueLampState(LampStateBase):
    def get_color(self):
        return 'Blue'


class Lamp(object):
    def __init__(self):
        self._current_state = None
        self._states = self.get_states()

    def get_states(self):
        return [GreenLampState(), RedLampState(), BlueLampState()]

    def next_state(self):
        if self._current_state is None:
            self._current_state = self._states[0]
        else:
            index = self._states.index(self._current_state)
            if index < len(self._states) - 1:
                index += 1
            else:
                index = 0
            self._current_state = self._states[index]
        return self._current_state

    def light(self):
        state = self.next_state()
        print state.get_color()


lamp = Lamp()
[lamp.light() for i in range(3)]
# Green
# Red
# Blue
[lamp.light() for i in range(3)]
# Green
# Red
# Blue

"""
Стратегия (Strategy) - паттерн поведения объектов.
Определяет семейство алгоритмов, инкапсулирует каждый из них и делает их взаимозаменяемыми.
Стратегия позволяет изменять алгоритмы независимо от клиентов, которые ими пользуются.
"""


class ImageDecoder(object):
    @staticmethod
    def decode(filename):
        raise NotImplementedError()


class PNGImageDecoder(ImageDecoder):
    @staticmethod
    def decode(filename):
        print 'PNG decode'


class JPEGImageDecoder(ImageDecoder):
    @staticmethod
    def decode(filename):
        print 'JPEG decode'


class GIFImageDecoder(ImageDecoder):
    @staticmethod
    def decode(filename):
        print 'GIF decode'


class Image(object):
    @classmethod
    def open(cls, filename):
        ext = filename.rsplit('.', 1)[-1]
        if ext == 'png':
            decoder = PNGImageDecoder
        elif ext in ('jpg', 'jpeg'):
            decoder = JPEGImageDecoder
        elif ext == 'gif':
            decoder = GIFImageDecoder
        else:
            raise RuntimeError('Невозможно декодировать файл %s' % filename)
        byterange = decoder.decode(filename)
        return cls(byterange, filename)

    def __init__(self, byterange, filename):
        self._byterange = byterange
        self._filename = filename


Image.open('picture.png')  # PNG decode
Image.open('picture.jpg')  # JPEG decode
Image.open('picture.gif')  # GIF decode

"""
*What is this pattern about?
Define a family of algorithms, encapsulate each one, and make them interchangeable.
Strategy lets the algorithm vary independently from clients that use it.
*TL;DR
Enables selecting an algorithm at runtime.
"""


class Order:
    def __init__(self, price, discount_strategy=None):
        self.price = price
        self.discount_strategy = discount_strategy

    def price_after_discount(self):
        if self.discount_strategy:
            discount = self.discount_strategy(self)
        else:
            discount = 0
        return self.price - discount

    def __repr__(self):
        fmt = "<Price: {}, price after discount: {}>"
        return fmt.format(self.price, self.price_after_discount())


def ten_percent_discount(order):
    return order.price * 0.10


def on_sale_discount(order):
    return order.price * 0.25 + 20


def main():
    """
    >>> Order(100)
    <Price: 100, price after discount: 100>
    >>> Order(100, discount_strategy=ten_percent_discount)
    <Price: 100, price after discount: 90.0>
    >>> Order(1000, discount_strategy=on_sale_discount)
    <Price: 1000, price after discount: 730.0>
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod()

"""
Шаблонный метод (Template method) - паттерн поведения классов.
Шаблонный метод определяет основу алгоритма и позволяет подклассам переопределить некоторые шаги алгоритма,
не изменяя его структуру в целом.
"""


class ExampleBase(object):
    def template_method(self):
        self.step_one()
        self.step_two()
        self.step_three()

    def step_one(self):
        raise NotImplementedError()

    def step_two(self):
        raise NotImplementedError()

    def step_three(self):
        raise NotImplementedError()


class Example(ExampleBase):
    def step_one(self):
        print 'Первый шаг алгоритма'

    def step_two(self):
        print 'Второй шаг алгоритма'

    def step_three(self):
        print 'Третий шаг алгоритма'


example = Example()
example.template_method()

# Первый шаг алгоритма
# Второй шаг алгоритма
# Третий шаг алгоритма

"""
An example of the Template pattern in Python
*TL;DR
Defines the skeleton of a base algorithm, deferring definition of exact
steps to subclasses.
*Examples in Python ecosystem:
Django class based views: https://docs.djangoproject.com/en/2.1/topics/class-based-views/
"""


def get_text():
    return "plain-text"


def get_pdf():
    return "pdf"


def get_csv():
    return "csv"


def convert_to_text(data):
    print("[CONVERT]")
    return "{} as text".format(data)


def saver():
    print("[SAVE]")


def template_function(getter, converter=False, to_save=False):
    data = getter()
    print("Got `{}`".format(data))

    if len(data) <= 3 and converter:
        data = converter(data)
    else:
        print("Skip conversion")

    if to_save:
        saver()

    print("`{}` was processed".format(data))


def main():
    """
    >>> template_function(get_text, to_save=True)
    Got `plain-text`
    Skip conversion
    [SAVE]
    `plain-text` was processed
    >>> template_function(get_pdf, converter=convert_to_text)
    Got `pdf`
    [CONVERT]
    `pdf as text` was processed
    >>> template_function(get_csv, to_save=True)
    Got `csv`
    Skip conversion
    [SAVE]
    `csv` was processed
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod()

"""
Постетитель (Visitor) - паттерн поведения объектов.
Описывает операцию, выполняемую с каждым объектом из некоторой структуры.
Паттерн посетитель позволяет определить новую операцию, не изменяя классы этих объектов.
"""


class FruitVisitor(object):
    """Посетитель"""
    def draw(self, fruit):
        methods = {
            Apple: self.draw_apple,
            Pear: self.draw_pear,
        }
        draw = methods.get(type(fruit), self.draw_unknown)
        draw(fruit)

    def draw_apple(self, fruit):
        print 'Яблоко'

    def draw_pear(self, fruit):
        print 'Груша'

    def draw_unknown(self, fruit):
        print 'Фрукт'


class Fruit(object):
    """Фрукты"""
    def draw(self, visitor):
        visitor.draw(self)


class Apple(Fruit):
    """Яблоко"""


class Pear(Fruit):
    """Груша"""


class Banana(Fruit):
    """Банан"""


visitor = FruitVisitor()

apple = Apple()
apple.draw(visitor)
# Яблоко

pear = Pear()
pear.draw(visitor)
# Груша

banana = Banana()
banana.draw(visitor)
# Фрукт

"""
http://peter-hoffmann.com/2010/extrinsic-visitor-pattern-python-inheritance.html
*TL;DR
Separates an algorithm from an object structure on which it operates.
An interesting recipe could be found in
Brian Jones, David Beazley "Python Cookbook" (2013):
- "8.21. Implementing the Visitor Pattern"
- "8.22. Implementing the Visitor Pattern Without Recursion"
*Examples in Python ecosystem:
- Python's ast.NodeVisitor: https://github.com/python/cpython/blob/master/Lib/ast.py#L250
which is then being used e.g. in tools like `pyflakes`.
- `Black` formatter tool implements it's own: https://github.com/ambv/black/blob/master/black.py#L718
"""


class Node:
    pass


class A(Node):
    pass


class B(Node):
    pass


class C(A, B):
    pass


class Visitor:
    def visit(self, node, *args, **kwargs):
        meth = None
        for cls in node.__class__.__mro__:
            meth_name = 'visit_' + cls.__name__
            meth = getattr(self, meth_name, None)
            if meth:
                break

        if not meth:
            meth = self.generic_visit
        return meth(node, *args, **kwargs)

    def generic_visit(self, node, *args, **kwargs):
        print('generic_visit ' + node.__class__.__name__)

    def visit_B(self, node, *args, **kwargs):
        print('visit_B ' + node.__class__.__name__)


def main():
    """
    >>> a, b, c = A(), B(), C()
    >>> visitor = Visitor()
    >>> visitor.visit(a)
    generic_visit A
    >>> visitor.visit(b)
    visit_B B
    >>> visitor.visit(c)
    visit_B C
    """


if __name__ == "__main__":
    import doctest
    doctest.testmod()