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#!/usr/bin/env python

# -*- coding: utf-8 -*-

"""

Implementation of the state pattern

http://ginstrom.com/scribbles/2007/10/08/design-patterns-python-style/

*TL;DR80

Implements state as a derived class of the state pattern interface.

Implements state transitions by invoking methods from the pattern's superclass.

"""

from __future__ import print_function

class State(object):

"""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(u"Scanning... Station is %s %s" % (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(u"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(u"Switching to AM")

self.radio.state = self.radio.amstate

class Radio(object):

"""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()

# Test our radio out

if __name__ == '__main__':

radio = Radio()

actions = [radio.scan] * 2 + [radio.toggle_amfm] + [radio.scan] * 2

actions *= 2

for action in actions:

action()

### OUTPUT ###

# 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