state.py

# ------------------------------
# State Design Pattern
# ------------------------------
# Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.

from abc import ABC, abstractmethod

class State(ABC):
    def handle_state(self):
        pass

class StateA(State):
    def handle_state(self):
        print('State changed to StateA.')

class StateB(State):
    def handle_state(self):
        print('State changed to StateB.')

class Context(State):
    def __init__(self):
        self.state = None

    def set_state(self, state):
        self.state = state

    def handle_state(self):
        self.state.handle_state()


context = Context()
stateA = StateA()
context.set_state(stateA)
context.handle_state()

print('-------------------------------------')

stateB = StateB()
context.set_state(stateB)
context.handle_state()