State

State Pattern 🔄

Overview 📖

The State Pattern allows an object to alter its behavior when its internal state changes. This pattern is used to encapsulate varying behavior for the same routine, based on the object's state object. It acts as a finite state machine.

Use Cases 🔍

• Workflow Management: Manage the state of an object across various states in a workflow, such as the stages of an order processing system.
• UI Controls: Different states of UI controls like buttons, checkboxes, etc., depending on user interactions.
• Permission Systems: Change object behavior based on permissions which can be seen as states.

Implementation 🛠️

The state.py file contains:

• A Context class, which maintains an instance of a ConcreteState subclass that defines the current state.
• An abstract State class that defines a common interface for all concrete states.
• Concrete State subclasses for each specific state, implementing the behavior associated with that state.

Example Usage 📝

class State:
    def handle(self, context):
        pass

class ConcreteStateA(State):
    def handle(self, context):
        print("State A handling context.")
        context.state = ConcreteStateB()

class ConcreteStateB(State):
    def handle(self, context):
        print("State B handling context.")
        context.state = ConcreteStateA()

class Context:
    def __init__(self, state):
        self.state = state

    def request(self):
        self.state.handle(self)

# Example usage
context = Context(ConcreteStateA())
context.request()  # Outputs: State A handling context.
context.request()  # Outputs: State B handling context.

Output 📊

State A handling context.
State B handling context.

This output demonstrates how the context transitions between states and changes behavior accordingly.

Business Logic Method 🧠

The State Pattern can be adapted to complex scenarios, such as a multistage approval process where different actions are taken based on the stage:

class ApprovalState(State):
    def handle(self, context):
        # Detailed implementation for approval handling
        print(f"Handling approval in state: {context.state.__class__.__name__}")

class ReviewState(State):
    def handle(self, context):
        print("In review state, moving to approval.")
        context.state = ApprovalState()

# Example usage
context = Context(ReviewState())
context.request()  # Outputs: In review state, moving to approval.
context.request()  # Outputs: Handling approval in state: ApprovalState

Testing 🧪

The test_state.py file should contain tests to ensure:

• State transitions occur as expected.
• Each state correctly executes its defined behavior.
• The context interacts with state objects properly.