python-patterns/state.py

"""Implementation of the state pattern"""  

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

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("Scanning... Station is", 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("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("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 = actions * 2 

    for action in actions:     
        action()