state.py

"""
Implementation of the state pattern

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

*TL;DR
Implements state as a derived class of the state pattern interface.
Implements state transitions by invoking methods from the pattern's superclass.
"""

from __future__ importannotations


classState:
"""Base state. This is to share functionality"""

defscan(self) ->None:
"""Scan the dial to the next station"""
self.pos+=1
ifself.pos==len(self.stations):
self.pos=0
print(f"Scanning... Station is {self.stations[self.pos]}{self.name}")


classAmState(State):
def__init__(self, radio: Radio) ->None:
self.radio=radio
self.stations= ["1250", "1380", "1510"]
self.pos=0
self.name="AM"

deftoggle_amfm(self) ->None:
print("Switching to FM")
self.radio.state=self.radio.fmstate


classFmState(State):
def__init__(self, radio: Radio) ->None:
self.radio=radio
self.stations= ["81.3", "89.1", "103.9"]
self.pos=0
self.name="FM"

deftoggle_amfm(self) ->None:
print("Switching to AM")
self.radio.state=self.radio.amstate


classRadio:
"""A radio. It has a scan button, and an AM/FM toggle switch."""

def__init__(self) ->None:
"""We have an AM state and an FM state"""
self.amstate=AmState(self)
self.fmstate=FmState(self)
self.state=self.amstate

deftoggle_amfm(self) ->None:
self.state.toggle_amfm()

defscan(self) ->None:
self.state.scan()


defmain():
"""
 >>> radio = Radio()
 >>> actions = [radio.scan] * 2 + [radio.toggle_amfm] + [radio.scan] * 2
 >>> actions *= 2

 >>> for action in actions:
 ... action()
 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
 """


if__name__=="__main__":
importdoctest

doctest.testmod()