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Python Patterns v0.2.0
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‎.gitignore

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#pdm.lock
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# pdm stores project-wide configurations in .pdm.toml, but it is recommended to not include it
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# in version control.
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# https://pdm.fming.dev/latest/usage/project/#working-with-version-control
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# https://pdm.fming.dev/#use-with-ide
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.pdm.toml
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.pdm-python
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.pdm-build/
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# PEP 582; used by e.g. github.com/David-OConnor/pyflow and github.com/pdm-project/pdm
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__pypackages__/
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# be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
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# and can be added to the global gitignore or merged into this file. For a more nuclear
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# option (not recommended) you can uncomment the following to ignore the entire idea folder.
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.idea/
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.idea/

‎LICENSE

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BSD 3-Clause License
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Copyright (c) 2024, A.A. Suvorov
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Copyright (c) 2021-2024, A.A. Suvorov
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:

‎README.md

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# Python Patterns
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A collection of design patterns and idioms in Python.
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***
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## Current Patterns
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__Creational Patterns__:
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| Pattern | Description |
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|:-------:| ----------- |
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| [Abstract Factory](patterns/creational/abstract_factory.py) | use a generic function with specific factories |
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| [Builder](patterns/creational/builder.py) | instead of using multiple constructors, builder receives parameters and returns constructed objects |
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| [Factory Method](patterns/creational/factory.py) | delegate a specialized function/method to create instances|
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| [Prototype](patterns/creational/prototype.py) | use a factory and clones of a prototype for new instances (if instantiation is expensive) |
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| [Singleton](patterns/creational/singleton.py) | Ensures that the class has only one instance, and provides a global access point to it. |
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__Structural Patterns__:
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| Pattern | Description |
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|:-------:| ----------- |
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| [Adapter](patterns/structural/adapter.py) | converts the interface of one class to the interface of another that clients expect. |
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| [Bridge](patterns/structural/bridge.py) | a client-provider middleman to soften interface changes |
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| [Composite](patterns/structural/composite.py) | lets clients treat individual objects and compositions uniformly |
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| [Decorator](patterns/structural/decorator.py) | wrap functionality with other functionality in order to affect outputs |
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| [Facade](patterns/structural/facade.py) | use one class as an API to a number of others |
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| [Flyweight](patterns/structural/flyweight.py) | transparently reuse existing instances of objects with similar/identical state |
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| [Proxy](patterns/structural/proxy.py) | an object funnels operations to something else |
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__Behavior Patterns__:
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| Pattern | Description |
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|:-------------------------------------------------------------------------:| ----------- |
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| [Blackboard](patterns/behavioral/blackboard.py) | architectural model, assemble different sub-system knowledge to build a solution, AI approach - non gang of four pattern. |
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| [Chain Of Responsibility](patterns/behavioral/chain_of_responsibility.py) | apply a chain of successive handlers to try and process the data. |
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| [Command](patterns/behavioral/command.py) | bundle a command and arguments to call later. |
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| [Interpreter](patterns/behavioral/interpreter.py) | a behavioral design pattern that solves a frequently encountered but subject to change problem. |
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| [Iterator](patterns/behavioral/iterator.py) | traverse a container and access the container's elements. |
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| [Mediator](patterns/behavioral/mediator.py) | an object that knows how to connect other objects and act as a proxy. |
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| [Memento](patterns/behavioral/memento.py) | generate an opaque token that can be used to go back to a previous state. |
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| [Observer](patterns/behavioral/observer.py) | provide a callback for notification of events/changes to data. |
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| [State](patterns/behavioral/state.py) | logic is organized into a discrete number of potential states and the next state that can be transitioned to. |
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| [Strategy](patterns/behavioral/strategy.py) | selectable operations over the same data. |
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| [Template Method](patterns/behavioral/template_method.py) |defines the basis of the algorithm and allows subclasses to override some of the steps in the algorithm, without changing its structure as a whole. |
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| [Visitor](patterns/behavioral/visitor.py) | invoke a callback for all items of a collection. |
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***
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## Disclaimer of liability:
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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***
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# --------------------------------------------------------
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# Licensed under the terms of the BSD 3-Clause License
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# (see LICENSE for details).
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# Copyright © 2018-2024, A.A Suvorov
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# All rights reserved.
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# --------------------------------------------------------

‎patterns/__init__.py

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# --------------------------------------------------------
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# Licensed under the terms of the BSD 3-Clause License
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# (see LICENSE for details).
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# Copyright © 2018-2024, A.A Suvorov
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# All rights reserved.
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# --------------------------------------------------------
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# https://github.com/smartlegionlab/
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# --------------------------------------------------------
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"""A collection of design patterns and idioms in Python"""

‎patterns/behavioral/__init__.py

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# --------------------------------------------------------
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# Licensed under the terms of the BSD 3-Clause License
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# (see LICENSE for details).
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# Copyright © 2018-2024, A.A Suvorov
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# All rights reserved.
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# --------------------------------------------------------
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# https://github.com/smartlegionlab/
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# --------------------------------------------------------

‎patterns/behavioral/blackboard.py

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# --------------------------------------------------------
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# Licensed under the terms of the BSD 3-Clause License
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# (see LICENSE for details).
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# Copyright © 2018-2024, A.A Suvorov
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# All rights reserved.
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# --------------------------------------------------------
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# https://github.com/smartlegionlab/
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# --------------------------------------------------------
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"""Black Board"""
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import abc
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import random
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class Blackboard:
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def __init__(self):
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self.experts = []
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self.common_state = {
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'problems': 0,
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'suggestions': 0,
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'contributions': [],
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'progress': 0
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}
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def add_expert(self, expert):
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self.experts.append(expert)
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class Controller:
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def __init__(self, black_board):
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self.blackboard = black_board
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def run_loop(self):
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while self.blackboard.common_state['progress'] < 100:
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for expert in self.blackboard.experts:
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if expert.is_eager_to_contribute:
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expert.contribute()
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return self.blackboard.common_state['contributions']
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class AbstractExpert:
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__metaclass__ = abc.ABCMeta
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def __init__(self, black_board):
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self.blackboard = black_board
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@property
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def is_eager_to_contribute(self):
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raise NotImplementedError('Must provide implementation in subclass.')
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@abc.abstractmethod
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def contribute(self):
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raise NotImplementedError('Must provide implementation in subclass.')
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class Student(AbstractExpert):
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@property
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def is_eager_to_contribute(self):
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return True
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def contribute(self):
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self.blackboard.common_state['problems'] += random.randint(1, 10)
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self.blackboard.common_state['suggestions'] += random.randint(1, 10)
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self.blackboard.common_state['contributions'] += [self.__class__.__name__]
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self.blackboard.common_state['progress'] += random.randint(1, 2)
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class Scientist(AbstractExpert):
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@property
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def is_eager_to_contribute(self):
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return random.randint(0, 1)
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def contribute(self):
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self.blackboard.common_state['problems'] += random.randint(10, 20)
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self.blackboard.common_state['suggestions'] += random.randint(10, 20)
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self.blackboard.common_state['contributions'] += [self.__class__.__name__]
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self.blackboard.common_state['progress'] += random.randint(10, 30)
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class Professor(AbstractExpert):
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@property
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def is_eager_to_contribute(self):
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return True if self.blackboard.common_state['problems'] > 100 else False
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def contribute(self):
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self.blackboard.common_state['problems'] += random.randint(1, 2)
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self.blackboard.common_state['suggestions'] += random.randint(10, 20)
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self.blackboard.common_state['contributions'] += [self.__class__.__name__]
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self.blackboard.common_state['progress'] += random.randint(10, 100)
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def main():
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blackboard = Blackboard()
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blackboard.add_expert(Student(blackboard))
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blackboard.add_expert(Scientist(blackboard))
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blackboard.add_expert(Professor(blackboard))
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c = Controller(blackboard)
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contributions = c.run_loop()
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from pprint import pprint
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pprint(contributions)
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if __name__ == '__main__':
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# Output:
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# ['Student',
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# 'Student',
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# 'Scientist',
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# 'Student',
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# 'Scientist',
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# 'Student',
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# 'Scientist',
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# 'Student',
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# 'Scientist',
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# 'Student',
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# 'Scientist',
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# 'Professor']
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main()

‎patterns/behavioral/chain_of_responsibility.py

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# --------------------------------------------------------
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# Licensed under the terms of the BSD 3-Clause License
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# (see LICENSE for details).
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# Copyright © 2018-2024, A.A Suvorov
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# All rights reserved.
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# --------------------------------------------------------
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# https://github.com/smartlegionlab/
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# --------------------------------------------------------
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"""Chain of responsibility"""
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class HttpHandler:
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def handle(self, code):
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raise NotImplementedError()
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class Http404Handler(HttpHandler):
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def handle(self, code):
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if code == 404:
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return 'Page not found'
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class Http500Handler(HttpHandler):
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def handle(self, code):
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if code == 500:
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return 'server error'
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class Client:
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def __init__(self):
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self._handlers = []
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def add_handler(self, h):
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self._handlers.append(h)
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def response(self, code):
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for h in self._handlers:
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msg = h.handle(code)
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if msg:
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print('Answer: %s' % msg)
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break
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else:
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print('Code not processed')
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def main():
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client = Client()
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client.add_handler(Http404Handler())
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client.add_handler(Http500Handler())
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client.response(400)
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client.response(404)
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client.response(500)
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if __name__ == '__main__':
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# Output:
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# Code not processed
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# Answer: Page not found
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# Answer: Server error
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main()

‎patterns/behavioral/command.py

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# --------------------------------------------------------
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# Licensed under the terms of the BSD 3-Clause License
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# (see LICENSE for details).
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# Copyright © 2018-2024, A.A Suvorov
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# All rights reserved.
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# --------------------------------------------------------
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# https://github.com/smartlegionlab/
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# --------------------------------------------------------
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"""Command"""
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from abc import ABC
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class Light:
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@staticmethod
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def turn_on():
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print('To turn on the light')
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@staticmethod
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def turn_off():
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print('Turn the lights off')
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class CommandBase:
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def execute(self):
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raise NotImplementedError()
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class LightCommandBase(CommandBase, ABC):
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def __init__(self, light_):
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self.light = light_
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class TurnOnLightCommand(LightCommandBase):
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def execute(self):
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self.light.turn_on()
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class TurnOffLightCommand(LightCommandBase):
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def execute(self):
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self.light.turn_off()
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class Switch:
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def __init__(self, on_cmd, off_cmd):
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self.on_cmd = on_cmd
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self.off_cmd = off_cmd
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def on(self):
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self.on_cmd.execute()
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def off(self):
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self.off_cmd.execute()
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def main():
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light = Light()
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switch = Switch(on_cmd=TurnOnLightCommand(light),
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off_cmd=TurnOffLightCommand(light))
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switch.on()
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switch.off()
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if __name__ == '__main__':
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# Output:
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# To turn on the light
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# Turn the lights off
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main()

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