python-design-patterns

python-design-patterns

python-design-patterns is a Python library that provides implementations of various design patterns. Currently, it includes an implementation of the Pipeline pattern, which allows for the processing of data through a series of steps.

Table of Contents

• python-design-patterns
  • Table of Contents
  • Installation
  • Usage
    • Pipeline Pattern
      • Examples
    • Memento Pattern
      • Examples
    • Mediator Pattern
      • Examples

Installation

To use this library, you need Python 3.9 or later installed on your machine. You can install the library using pip.

pip install python-design-patterns

Usage

Pipeline Pattern

The Pipeline pattern allows you to pass data through multiple processing steps. Each step can take inputs, perform operations, and pass results to the next step.

Examples

Here is a simple example of how to use the pipeline:

from pdp.pipeline import Pipeline, Step

# Define your processing functions
def add(x, y):
    return x + y

def compute(step1, x, z):
    return step1 + x - z

# Create a pipeline and add steps

steps = [
    Step(name="step1", func=add),
    Step(name="step2", func=compute),
]

pipeline = Pipeline(steps)

# Run the pipeline
result = pipeline.run(x=1, y=2, z=3)
print(result)  # Output: {'x': 1, 'y': 2, 'z': 3, 'step1': 3, 'step2': 1}

Here are some additional examples to demonstrate the capabilities of the Pipeline pattern:

def multiply(x, y):
    return x * y

def subtract(step1, z):
    return step1 - z

# Create a new pipeline
pipeline = Pipeline()
pipeline.add_step(Step(name="step1", func=multiply))
pipeline.add_step(Step(name="step2", func=subtract))

# Run the pipeline
result = pipeline.run(x=2, y=3, z=1)
print(result)  # Output: {'x': 2, 'y': 3, 'z': 1, 'step1': 6, 'step2': 5}

Memento Pattern

The Memento pattern allows you to save and restore the state of an object without exposing its internal structure. It is useful for implementing features like undo/redo in applications.

Examples

Here's a simple example of how to use the Memento pattern: To use this pattern, your class should inherit from the BaseOriginator class provided by the library.

from pdp.memento import BaseOriginator, Caretaker

# Define your own class that you want to be able to save/restore
class Mobility(BaseOriginator):
    def __init__(self):
        self.x = 1
        self.y = 2
        self.speed = 26

    # override get and restore state
    def get_state(self): 
        return {
            'x': self.x,
            'y': self.y,
            'speed': self.speed
        }

    def set_state(self, state):
        self.x = state['x']
        self.y = state['y']
        self.speed = state['speed']
    
    def __str__(self):
        return f"x={self.x}, y={self.y}, speed={self.speed}"

car = Mobility()
caretaker = Caretaker(car)

# save state
print(car) # x=1, y=2, speed=26
caretaker.save()

# change state
car.x = 5
car.y = 10
car.speed = 50
print(car) # x=5, y=10, speed=50

# save new state
caretaker.save()

# change state
car.x = 10
car.y = 20
car.speed = 100
print(car) # x=10, y=20, speed=100

# restore to previous state saved
caretaker.undo()
print(car) # x=5, y=10, speed=50

# restore to saved index
caretaker.restore(0)
print(car) # x=1, y=2, speed=26

# save history to file
caretaker.save_to_file("car_history.json")

Mediator Pattern

Mediator is a behavioral design pattern that lets you reduce chaotic dependencies between objects. The pattern restricts direct communications between the objects and forces them to collaborate only via a mediator object.

Examples

Here's a simple example of how to use the Mediator pattern: To use this pattern, your class should inherit from the BaseComponent class provided by the library.

from pdp.mediator import Mediator, BaseComponent

class Button(BaseComponent):
    def __init__(self, name: str, mediator: Mediator):
        super().__init__(name, mediator)

    def click(self):
        self.notify({"value": "toto"})
    
    def on_notify(self, sender: BaseComponent, event: dict, *args, **kwargs):
        pass
    

class TextBox(BaseComponent):
    def __init__(self, name: str, mediator: Mediator):
        super().__init__(name, mediator)
        self.text = "default"

    def on_notify(self, sender: BaseComponent, event: dict, *args, **kwargs):
        if sender.name == "Button":
            self.text = event["value"]
    
    def show_text(self):
        print(self.text)


mediator = Mediator()

button = Button("Button", mediator)
textbox = TextBox("TextBox", mediator)

mediator.add_components(button, textbox)

textbox.show_text() # > "default"

button.click()
textbox.show_text() # > "toto"